Distributed semaphore with atomic updates

ABSTRACT

Methods and systems for allocating disk space and other limited resources (e.g., network bandwidth) for a cluster of data storage nodes using distributed semaphores with atomic updates are described. The distributed semaphores may be built on top of a distributed key-value store and used to reserve disk space, global disk streams for writing data to disks, and per node network bandwidth settings. A distributed semaphore comprising two or more semaphores that are accessed with different keys may be used to reduce contention and allow a globally accessible semaphore to scale as the number of data storage nodes within the cluster increases over time. In some cases, the number of semaphores within the distributed semaphore may be dynamically adjusted over time and may be set based on the total amount of disk space within the cluster and/or the number of contention fails that have occurred to the distributed semaphore.

BACKGROUND

Virtualization allows virtual hardware to be created and decoupled fromthe underlying physical hardware. For example, a hypervisor running on ahost machine or server may be used to create one or more virtualmachines that may each run the same operating system or differentoperating systems (e.g., a first virtual machine may run a Windows®operating system and a second virtual machine may run a Unix-likeoperating system such as OSX®). A virtual machine may comprise asoftware implementation of a physical machine. The virtual machine mayinclude one or more virtual hardware devices, such as a virtualprocessor, a virtual memory, a virtual disk, or a virtual networkinterface card. The virtual machine may load and execute an operatingsystem and applications from the virtual memory. The operating systemand applications executed by the virtual machine may be stored using thevirtual disk. The virtual machine may be stored (e.g., using a datastorecomprising one or more physical storage devices) as a set of filesincluding a virtual disk file for storing the contents of the virtualdisk and a virtual machine configuration file for storing configurationsettings for the virtual machine. The configuration settings may includethe number of virtual processors (e.g., four virtual CPUs), the size ofa virtual memory, and the size of a virtual disk (e.g., a 10 GB virtualdisk) for the virtual machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts one embodiment of a networked computing environment.

FIG. 1B depicts one embodiment of a server.

FIG. 1C depicts one embodiment of a storage appliance.

FIG. 1D depicts one embodiment of a portion of an integrated datamanagement and storage system that includes a plurality of nodes incommunication with each other and one or more storage devices.

FIGS. 2A-2Q depict various embodiments of sets of files and datastructures associated with managing and storing snapshots of virtualmachines.

FIG. 3A is a flowchart describing one embodiment of a process formanaging and storing virtual machine snapshots using a data storagesystem.

FIG. 3B is a flowchart describing one embodiment of a process fordetermining the type of snapshot to be stored using a data storagesystem.

FIG. 3C is a flowchart describing one embodiment of a process forrestoring a version of a virtual machine using a data storage system.

FIG. 4A depicts one embodiment of a distributed semaphore comprisingthree semaphores for reserving disk space that may be allocated to jobsrunning on data storage nodes within a cluster.

FIG. 4B depicts one embodiment of a distributed semaphore comprisingfour semaphores for reserving disk space accessible by data storagenodes within a cluster.

FIG. 4C depicts another embodiment of a distributed semaphore comprisingfour semaphores for reserving disk space accessible by data storagenodes within a cluster.

FIG. 4D depicts one embodiment of a distributed semaphore comprising sixsemaphores for reserving disk space accessible by data storage nodeswithin a cluster.

FIG. 4E depicts one embodiment of the distributed semaphore depicted inFIG. 4A with fixed-size chunks per semaphore.

FIG. 4F depicts another embodiment of the distributed semaphore depictedin FIG. 4A with different-sized chunks per semaphore.

FIG. 4G depicts one embodiment of the distributed semaphore depicted inFIG. 4E over time as disk space for a job is reserved.

FIG. 5A depicts one embodiment of initial mappings from jobs to initialsemaphores.

FIG. 5B depicts another embodiment of initial mappings from jobs toinitial semaphores.

FIG. 6A is a flowchart describing one embodiment of a process forallocating disk space using a distributed semaphore.

FIGS. 6B-6C depict a flowchart describing another embodiment of aprocess for allocating disk space using a distributed semaphore.

FIG. 7A is a flowchart describing one embodiment of a process forallocating disk space using a distributed semaphore.

FIG. 7B is a flowchart describing another embodiment of a process forallocating disk space using a distributed semaphore.

DETAILED DESCRIPTION

Technology is described for allocating disk space and other limitedresources (e.g., network bandwidth) for a cluster of data storage nodesusing distributed semaphores with atomic updates. The distributedsemaphores may be built on top of a distributed key-value store and usedto reserve disk space (e.g., for a job capturing a snapshot of a virtualmachine or consolidating snapshots associated with different point intime versions of the virtual machine), reserve global disk streams forwriting data to disks, reserve memory (e.g., RAM), and reserve per nodenetwork bandwidth settings for data storage nodes in the cluster. Oneissue with using a single global semaphore with a single row that isaccessed by a single key is that contention issues on the underlyingkey-value store may prevent efficient reservations and releases fromoccurring, especially when numerous jobs are vying for access to thesame single row at the same time. Instead, a distributed semaphorecomprising two or more semaphores that are accessed with different keysmay be used to reduce contention and allow the global semaphore to scaleas the number of data storage nodes within the cluster increases overtime. The two or more semaphores of the distributed semaphore withdifferent keys may together represent the entire global semaphore. Inone example, the distributed semaphore may correspond with disk spacereservations and may be used to reserve ten different portions of a diskspace for storing electronic files associated with various jobs runningwithin the cluster of data storage nodes. In this case, the distributedsemaphore may comprise ten different semaphores, wherein each semaphoreof the ten semaphores corresponds with one of the ten portions of thedisk space (e.g., each portion may cover 10 TB of a 100 TB disk space).

In some embodiments, a distributed semaphore may be used to reserve diskspace for a job prior to the job performing various tasks in order toprevent the job from running out of disk space half-way throughperformance of the various tasks. The various tasks may includeconsolidating two or more snapshots of a real or virtual machine,generating and storing a reverse incremental file associated with asnapshot of a real or virtual machine, or generating and storing afull-image point in time version of a real or virtual machine. When ajob (or a computing process) requires an amount of disk space to beallocated, the job may attempt to reserve the entire amount of diskspace from an initial semaphore (e.g., which may be identified randomlyfrom among the multiple semaphores of the distributed semaphore oridentified as the semaphore to which a job identifier for the job hashesto or maps to) of a plurality of semaphores for the distributedsemaphore. If the job (or a disk space allocation process working onbehalf of the job) cannot reserve the entire amount of disk spacerequired by the job from the initial semaphore, then the job mayidentify a subset of the plurality of semaphores and compute anallocation between the semaphores of the subset of the plurality ofsemaphores that best balances the disk space allocations for each of thesemaphores in the subset. In one example, the allocation between thesemaphores of the subset may be computed using a water-filling algorithmwith fixed-size reserved chunks per semaphore. One reason to notcompletely fill-up each semaphore of the subset is to leave disk spacecorresponding with the reserved chunk size for other jobs that directlymap to those semaphores as initial semaphores (e.g., the initialsemaphores to which those other jobs first hash); otherwise, thesefailed allocations will lead to more pressure on other semaphores whichmay narrow down the set of semaphores to which it is possible toallocate and exacerbate the contention issue. In this case, the subsetof the plurality of semaphores may be sorted or ranked based on theamount of disk space available to be reserved or allocated per eachsemaphore and the least full semaphore of the subset may be filled untilthe amount of disk space per semaphore minus the reserved chunk size isreserved or the entire amount of disk space that is required for the jobis reserved. If the least full semaphore cannot be used to reserve theentire amount of disk space required for the job, then the subset may besorted again and the least full semaphore of the subset may beidentified and filled until the amount of disk space for the least fullsemaphore minus the reserved chunk size is reached or the entire amountof disk space that is required for the job is reserved.

In one example, a job may need to reserve 500 GB of disk space or have500 GB of disk space allocated for the job, the subset of the pluralityof semaphores may comprise three semaphores associated with allocating 1TB of disk space each, and the reserved chunk size may comprise 100 GB.For the three semaphores, a first semaphore of the three semaphores mayhave already been used to reserve 600 GB of disk space, a secondsemaphore of the three semaphores may have already been used to reserve700 GB of disk space, and a third semaphore of the three semaphores mayhave already been used to reserve 800 GB of disk space. In this case,the least full semaphore of the subset comprises the first semaphore sothe job (or a disk space allocation process working on behalf of thejob) may reserve 300 GB of disk space from the first semaphore in orderto leave 100 GB of disk space still available for the first semaphoreand then reserve 200 GB of disk space from the second semaphore.

In some embodiments, the number of semaphores within a distributedsemaphore may be dynamically adjusted over time and may be set ordetermined based on the total amount of disk space within the cluster,the total amount of available disk space within the cluster that isavailable for allocation to jobs to be executed within the cluster, thetotal number of nodes within the cluster, and/or the number ofcontention fails that have occurred during a particular time period(e.g., within the past thirty minutes). The number of contention failsmay comprise the number of jobs that failed due to not being able toaccess the distributed semaphore or the number of jobs that failed toreserve disk space using the distributed semaphore due to contention forsemaphores of the distributed semaphore. In one example, the number ofsemaphores may be determined such that each semaphore within thedistributed semaphore corresponds with reservations for a fixed amountof disk space (e.g., each semaphore may correspond with reserving 10 TBsof disk space); in this case, the number of semaphores may be equal tothe total amount of disk space for the cluster divided by the fixedamount of disk space per semaphore. In another example, the number ofsemaphores may comprise two times the number of nodes within thecluster. In another example, the number of semaphores may be set suchthat the number of contention fails over the particular time period isbelow an upper threshold for the number of contention failures; in thiscase, the number of semaphores may be increased such that the number ofcontention fails is reduced to less than the upper threshold (e.g., isnot more than twenty) over a preceding period of time (e.g., over thepast ten minutes). In another example, the number of semaphores may beincreased if the number of contention fails over the particular timeperiod is above a threshold number of failures (e.g., is greater thantwenty). In another example, the number of semaphores may be decreasedif the number of contention fails over the particular time period isbelow a lower threshold (e.g., is less than five) for the number ofcontention failures; in this case, the number of semaphores may bedecreased if the number of contention fails is less than five over thepast ten minutes. Increased fragmentation may increase the amount oftime it takes to make a reservation or release since the number of calls(e.g., linear in the number of semaphores) that must be made to thekey-value store may increase. Decreasing the number of semaphores mayhelp to reduce fragmentation and improve performance of the system.

In other embodiments, the number of semaphores within the distributedsemaphore may be fixed, but the amount of disk space that may bereserved per semaphore may be set based on the total amount of diskspace within the cluster. In one example, the number of semaphores maybe set to ten and the amount of disk space that may be reserved persemaphore may be equal to the total amount of disk space for the clusterdivided by ten. In this case, the amount of reservable disk space persemaphore may be evenly divided among the ten semaphores.

In some embodiments, a semaphore of a plurality of semaphores for thedistributed semaphore may correspond with one or more chunks (orindividually reservable data partitions). In one example, the semaphoremay correspond with reserving 10 TBs of disk space and the semaphore maycorrespond with ten different chunks, wherein each of the ten chunkscorresponds with 1 TB of disk space out of the 10 TBs of disk space forthe semaphore. In some cases, when a job reserves disk space from thesemaphore, the job may make reservations at the granularity of thechunks. For example, if the job must reserve 3.5 TBs of disk space fromthe semaphore, then the job may have to reserve four of the 1 TB chunks.The sizes of the data chunks for the semaphore may be dynamicallyadjusted over time and set based on the amount of disk space remainingto be reserved by the semaphore and/or the total amount of availabledisk space within a cluster of data storage nodes. In one example, ifless than a threshold amount of disk space may be reserved from asemaphore (e.g., the semaphore has less than 2 TB of disk space left toreserve out of a total of 10 TBs), then the number of chunks may beincreased (e.g., doubled) such that the amount of disk space per chunkis reduced. In another example, if less than a threshold amount of diskspace is available to be allocated within the cluster (e.g., there isless than 200 TBs of available disk space), then the number of chunksfor each of the semaphores of the distributed semaphore may be increased(e.g., doubled) such that the amount of disk space per chunk is reduced.In another example, if more than a threshold amount of disk space may bereserved from a semaphore (e.g., the semaphore has more than 8 TB ofdisk space left to reserve out of a total of 10 TBs), then the number ofchunks may be decreased (e.g., cut in half) such that the amount of diskspace per chunk is increased.

In some cases, when a job reserves an amount of disk space from asemaphore of the distributed semaphore, the disk space reserved mayfirst be marked as pending (e.g., one or more chunks of the semaphoremay be set into a pending state) and the job may not finalize thereservation of the disk space until the job is able to reserve theentire amount of disk space necessary for the job. The job may finalizethe reservation of the disk space by setting one or more chunks of thesemaphore into a taken state or a reserved state. In the event that thejob fails (e.g., due to a node failure) and disk space marked as pendinghas been pending for more than a threshold period of time (e.g., morethan two minutes), then a cleanup job may be used to change the diskspace marked as pending back to available or unreserved. Cleanup jobs toreclaim disk space marked as pending for more than the threshold amountof time may be run on a periodic basis (e.g., every thirty minutes). Thecleanup jobs may be run more frequently (e.g., every ten minutes) if theamount of available disk space has fallen below a threshold amount ofdisk space (e.g., if the amount of available disk space for a cluster isless than ten percent of the total disk space or is less than 10 TB ofdisk space). A second job that is attempting to reserve disk space froma semaphore may reserve disk space that was marked as pending if thepending reservation for the disk space has been pending for more thanthe threshold period of time. In this case, subsequent jobs may be usedto reclaim disk space and reserve the disk space for the subsequent jobsif one or more chunks of the semaphore have been marked as pending formore than the threshold period of time.

In some embodiments, a distributed semaphore may be used to reservenetwork bandwidth for the nodes in a cluster. Per-node networkbandwidths may be throttled or adjusted over time to maximize theaggregate bandwidth of the cluster without exceeding a global bandwidthallowance for the entire cluster. The throttling of the individual nodenetwork bandwidths may include periodically adjusting individual nodebandwidth settings for each node of a plurality of nodes within thecluster using node network interfaces. In some cases, a node of theplurality of nodes may determine an amount of node bandwidth requiredfor the node based on the number of jobs running on the node or thenumber of tokens assigned to jobs running on the node and reserve theamount of node bandwidth for the node using a distributed semaphore forreserving node bandwidth from a global bandwidth allowance for theentire cluster. More information about throttling per-node networkbandwidths may be found in U.S. patent application Ser. No. 15/658,348,entitled “Throttling Network Bandwidth Using Per-Node NetworkInterfaces,” filed Jul. 24, 2017, which is herein incorporated byreference in its entirety.

An integrated data management and storage system may be configured tomanage the automated storage, backup, deduplication, replication,recovery, and archival of data within and across physical and virtualcomputing environments. The integrated data management and storagesystem may provide a unified primary and secondary storage system withbuilt-in data management that may be used as both a backup storagesystem and a “live” primary storage system for primary workloads. Insome cases, the integrated data management and storage system may managethe extraction and storage of historical snapshots associated withdifferent point in time versions of virtual machines and/or realmachines (e.g., a hardware server, a laptop, a tablet computer, asmartphone, or a mobile computing device) and provide near instantaneousrecovery of a backed-up version of a virtual machine, a real machine, orone or more files residing on the virtual machine or the real machine.The integrated data management and storage system may allow backed-upversions of real or virtual machines to be directly mounted or madeaccessible to primary workloads in order to enable the nearinstantaneous recovery of the backed-up versions and allow secondaryworkloads (e.g., workloads for experimental or analytics purposes) todirectly use the integrated data management and storage system as aprimary storage target to read or modify past versions of data.

The integrated data management and storage system may include adistributed cluster of storage nodes that presents itself as a unifiedstorage system even though numerous storage nodes may be connectedtogether and the number of connected storage nodes may change over timeas storage nodes are added to or removed from the cluster. Theintegrated data management and storage system may utilize a scale-outnode based architecture in which a plurality of data storage appliancescomprising one or more nodes are in communication with each other viaone or more networks. Each storage node may include two or moredifferent types of storage devices and control circuitry configured tostore, deduplicate, compress, and/or encrypt data stored using the twoor more different types of storage devices. In one example, a storagenode may include two solid-state drives (SSDs), three hard disk drives(HDDs), and one or more processors configured to concurrently read datafrom and/or write data to the storage devices. The integrated datamanagement and storage system may replicate and distribute versioneddata, metadata, and task execution across the distributed cluster toincrease tolerance to node and disk failures (e.g., snapshots of avirtual machine may be triply mirrored across the cluster). Datamanagement tasks may be assigned and executed across the distributedcluster in a fault tolerant manner based on the location of data withinthe cluster (e.g., assigning tasks to nodes that store data related tothe task) and node resource availability (e.g., assigning tasks to nodeswith sufficient compute or memory capacity for the task).

The integrated data management and storage system may apply a databackup and archiving schedule to backed-up real and virtual machines toenforce various backup service level agreements (SLAs), recovery pointobjectives (RPOs), recovery time objectives (RTOs), data retentionrequirements, and other data backup, replication, and archival policiesacross the entire data lifecycle. For example, the data backup andarchiving schedule may require that snapshots of a virtual machine arecaptured and stored every four hours for the past week, every day forthe past six months, and every week for the past five years.

As virtualization technologies are adopted into information technology(IT) infrastructures, there is a growing need for recovery mechanisms tosupport mission critical application deployment within a virtualizedinfrastructure. However, a virtualized infrastructure may present a newset of challenges to the traditional methods of data management due tothe higher workload consolidation and the need for instant, granularrecovery. The benefits of using an integrated data management andstorage system include the ability to reduce the amount of data storagerequired to backup real and virtual machines, the ability to reduce theamount of data storage required to support secondary or non-productionworkloads, the ability to provide a non-passive storage target in whichbackup data may be directly accessed and modified, and the ability toquickly restore earlier versions of virtual machines and files storedlocally or in the cloud.

FIG. 1A depicts one embodiment of a networked computing environment 100in which the disclosed technology may be practiced. As depicted, thenetworked computing environment 100 includes a data center 150, astorage appliance 140, and a computing device 154 in communication witheach other via one or more networks 180. The networked computingenvironment 100 may include a plurality of computing devicesinterconnected through one or more networks 180. The one or morenetworks 180 may allow computing devices and/or storage devices toconnect to and communicate with other computing devices and/or otherstorage devices. In some cases, the networked computing environment mayinclude other computing devices and/or other storage devices not shown.The other computing devices may include, for example, a mobile computingdevice, a non-mobile computing device, a server, a workstation, a laptopcomputer, a tablet computer, a desktop computer, or an informationprocessing system. The other storage devices may include, for example, astorage area network storage device, a networked-attached storagedevice, a hard disk drive, a solid-state drive, or a data storagesystem. The one or more networks 180 may include a cellular network, amobile network, a wireless network, a wired network, a secure networksuch as an enterprise private network, an unsecure network such as awireless open network, a local area network (LAN), a wide area network(WAN), and the Internet.

The data center 150 may include one or more servers, such as server 160,in communication with one or more storage devices, such as storagedevice 156. The one or more servers may also be in communication withone or more storage appliances, such as storage appliance 170. Theserver 160, storage device 156, and storage appliance 170 may be incommunication with each other via a networking fabric connecting serversand data storage units within the data center to each other. The server160 may comprise a production hardware server. The storage appliance 170may include a data management system for backing up virtual machines,real machines, virtual disks, real disks, and/or electronic files withinthe data center 150. The server 160 may be used to create and manage oneor more virtual machines associated with a virtualized infrastructure.The one or more virtual machines may run various applications, such as adatabase application or a web server. The storage device 156 may includeone or more hardware storage devices for storing data, such as a harddisk drive (HDD), a magnetic tape drive, a solid-state drive (SSD), astorage area network (SAN) storage device, or a networked-attachedstorage (NAS) device. In some cases, a data center, such as data center150, may include thousands of servers and/or data storage devices incommunication with each other. The data storage devices may comprise atiered data storage infrastructure (or a portion of a tiered datastorage infrastructure). The tiered data storage infrastructure mayallow for the movement of data across different tiers of a data storageinfrastructure between higher-cost, higher-performance storage devices(e.g., solid-state drives and hard disk drives) and relativelylower-cost, lower-performance storage devices (e.g., magnetic tapedrives).

A server, such as server 160, may allow a client to download informationor files (e.g., executable, text, application, audio, image, or videofiles) from the server or to perform a search query related toparticular information stored on the server. In some cases, a server mayact as an application server or a file server. In general, a server mayrefer to a hardware device that acts as the host in a client-serverrelationship or a software process that shares a resource with orperforms work for one or more clients. One embodiment of server 160includes a network interface 165, processor 166, memory 167, disk 168,and virtualization manager 169 all in communication with each other.Network interface 165 allows server 160 to connect to one or morenetworks 180. Network interface 165 may include a wireless networkinterface and/or a wired network interface. Processor 166 allows server160 to execute computer readable instructions stored in memory 167 inorder to perform processes described herein. Processor 166 may includeone or more processing units, such as one or more CPUs and/or one ormore GPUs. Memory 167 may comprise one or more types of memory (e.g.,RAM, SRAM, DRAM, ROM, EEPROM, Flash, etc.). Disk 168 may include a harddisk drive and/or a solid-state drive. Memory 167 and disk 168 maycomprise hardware storage devices.

The virtualization manager 169 may manage a virtualized infrastructureand perform management operations associated with the virtualizedinfrastructure. For example, the virtualization manager 169 may managethe provisioning of virtual machines running within the virtualizedinfrastructure and provide an interface to computing devices interactingwith the virtualized infrastructure. The virtualization manager 169 mayalso perform various virtual machine related tasks, such as cloningvirtual machines, creating new virtual machines, monitoring the state ofvirtual machines, moving virtual machines between physical hosts forload balancing purposes, and facilitating backups of virtual machines.

One embodiment of storage appliance 170 includes a network interface175, processor 176, memory 177, and disk 178 all in communication witheach other. Network interface 175 allows storage appliance 170 toconnect to one or more networks 180. Network interface 175 may include awireless network interface and/or a wired network interface. Processor176 allows storage appliance 170 to execute computer readableinstructions stored in memory 177 in order to perform processesdescribed herein. Processor 176 may include one or more processingunits, such as one or more CPUs and/or one or more GPUs. Memory 177 maycomprise one or more types of memory (e.g., RAM, SRAM, DRAM, ROM,EEPROM, NOR Flash, NAND Flash, etc.). Disk 178 may include a hard diskdrive and/or a solid-state drive. Memory 177 and disk 178 may comprisehardware storage devices.

In one embodiment, the storage appliance 170 may include four machines.Each of the four machines may include a multi-core CPU, 64 GB of RAM, a400 GB SSD, three 4 TB HDDs, and a network interface controller. In thiscase, the four machines may be in communication with the one or morenetworks 180 via the four network interface controllers. The fourmachines may comprise four nodes of a server cluster. The server clustermay comprise a set of physical machines that are connected together viaa network. The server cluster may be used for storing data associatedwith a plurality of virtual machines, such as backup data associatedwith different point in time versions of one or more virtual machines.

In another embodiment, the storage appliance 170 may comprise a virtualappliance that comprises four virtual machines. Each of the virtualmachines in the virtual appliance may have 64 GB of virtual memory, a 12TB virtual disk, and a virtual network interface controller. In thiscase, the four virtual machines may be in communication with the one ormore networks 180 via the four virtual network interface controllers.The four virtual machines may comprise four nodes of a virtual cluster.

The networked computing environment 100 may provide a cloud computingenvironment for one or more computing devices. In one embodiment, thenetworked computing environment 100 may include a virtualizedinfrastructure that provides software, data processing, and/or datastorage services to end users accessing the services via the networkedcomputing environment. In one example, networked computing environment100 may provide cloud-based work productivity or business relatedapplications to a computing device, such as computing device 154. Thecomputing device 154 may comprise a mobile computing device or a tabletcomputer. The storage appliance 140 may comprise a cloud-based datamanagement system for backing up virtual machines and/or files within avirtualized infrastructure, such as virtual machines running on server160 or files stored on server 160.

In some embodiments, the storage appliance 170 may manage the extractionand storage of virtual machine snapshots associated with different pointin time versions of one or more virtual machines running within the datacenter 150. A snapshot of a virtual machine may correspond with a stateof the virtual machine at a particular point in time. In some cases, thesnapshot may capture the state of various virtual machine settings andthe state of one or more virtual disks for the virtual machine. Inresponse to a restore command from the server 160, the storage appliance170 may restore a point in time version of a virtual machine or restorepoint in time versions of one or more files located on the virtualmachine and transmit the restored data to the server 160. In response toa mount command from the server 160, the storage appliance 170 may allowa point in time version of a virtual machine to be mounted and allow theserver 160 to read and/or modify data associated with the point in timeversion of the virtual machine. To improve storage density, the storageappliance 170 may deduplicate and compress data associated withdifferent versions of a virtual machine and/or deduplicate and compressdata associated with different virtual machines. To improve systemperformance, the storage appliance 170 may first store virtual machinesnapshots received from a virtualized environment in a cache, such as aflash-based cache. The cache may also store popular data or frequentlyaccessed data (e.g., based on a history of virtual machinerestorations), incremental files associated with commonly restoredvirtual machine versions, and current day incremental files orincremental files corresponding with snapshots captured within the past24 hours.

An incremental file may comprise a forward incremental file or a reverseincremental file. A forward incremental file may include a set of datarepresenting changes that have occurred since an earlier point in timesnapshot of a virtual machine. To generate a snapshot of the virtualmachine corresponding with a forward incremental file, the forwardincremental file may be combined with an earlier point in time snapshotof the virtual machine (e.g., the forward incremental file may becombined with the last full image of the virtual machine that wascaptured before the forward incremental was captured and any otherforward incremental files that were captured subsequent to the last fullimage and prior to the forward incremental file). A reverse incrementalfile may include a set of data representing changes from a later pointin time snapshot of a virtual machine. To generate a snapshot of thevirtual machine corresponding with a reverse incremental file, thereverse incremental file may be combined with a later point in timesnapshot of the virtual machine (e.g., the reverse incremental file maybe combined with the most recent snapshot of the virtual machine and anyother reverse incremental files that were captured prior to the mostrecent snapshot and subsequent to the reverse incremental file).

The storage appliance 170 may provide a user interface (e.g., aweb-based interface or a graphical user interface) that displays virtualmachine information, such as identifications of the virtual machinesprotected and the historical versions or time machine views for each ofthe virtual machines protected, and allows an end user to search,select, and control virtual machines managed by the storage appliance. Atime machine view of a virtual machine may include snapshots of thevirtual machine over a plurality of points in time. Each snapshot maycomprise the state of the virtual machine at a particular point in time.Each snapshot may correspond with a different version of the virtualmachine (e.g., Version 1 of a virtual machine may correspond with thestate of the virtual machine at a first point in time and Version 2 ofthe virtual machine may correspond with the state of the virtual machineat a second point in time subsequent to the first point in time).

FIG. 1B depicts one embodiment of server 160 in FIG. 1A. The server 160may comprise one server out of a plurality of servers that are networkedtogether within a data center. In one example, the plurality of serversmay be positioned within one or more server racks within the datacenter. As depicted, the server 160 includes hardware-level componentsand software-level components. The hardware-level components include oneor more processors 182, one or more memory 184, and one or more disks185. The software-level components include a hypervisor 186, avirtualized infrastructure manager 199, and one or more virtualmachines, such as virtual machine 198. The hypervisor 186 may comprise anative hypervisor or a hosted hypervisor. The hypervisor 186 may providea virtual operating platform for running one or more virtual machines,such as virtual machine 198. Virtual machine 198 includes a plurality ofvirtual hardware devices including a virtual processor 192, a virtualmemory 194, and a virtual disk 195. The virtual disk 195 may comprise afile stored within the one or more disks 185. In one example, a virtualmachine may include a plurality of virtual disks, with each virtual diskof the plurality of virtual disks associated with a different filestored on the one or more disks 185. Virtual machine 198 may include aguest operating system 196 that runs one or more applications, such asapplication 197. The virtualized infrastructure manager 199, which maycorrespond with the virtualization manager 169 in FIG. 1A, may run on avirtual machine or natively on the server 160. The virtualizedinfrastructure manager 199 may provide a centralized platform formanaging a virtualized infrastructure that includes a plurality ofvirtual machines.

In one embodiment, the server 160 may use the virtualized infrastructuremanager 199 to facilitate backups for a plurality of virtual machines(e.g., eight different virtual machines) running on the server 160. Eachvirtual machine running on the server 160 may run its own guestoperating system and its own set of applications. Each virtual machinerunning on the server 160 may store its own set of files using one ormore virtual disks associated with the virtual machine (e.g., eachvirtual machine may include two virtual disks that are used for storingdata associated with the virtual machine).

In one embodiment, a data management application running on a storageappliance, such as storage appliance 140 in FIG. 1A or storage appliance170 in FIG. 1A, may request a snapshot of a virtual machine running onserver 160. The snapshot of the virtual machine may be stored as one ormore files, with each file associated with a virtual disk of the virtualmachine. A snapshot of a virtual machine may correspond with a state ofthe virtual machine at a particular point in time. The particular pointin time may be associated with a time stamp. In one example, a firstsnapshot of a virtual machine may correspond with a first state of thevirtual machine (including the state of applications and files stored onthe virtual machine) at a first point in time (e.g., 6:30 p.m. on Jun.29, 2017) and a second snapshot of the virtual machine may correspondwith a second state of the virtual machine at a second point in timesubsequent to the first point in time (e.g., 6:30 p.m. on Jun. 30,2017).

In response to a request for a snapshot of a virtual machine at aparticular point in time, the virtualized infrastructure manager 199 mayset the virtual machine into a frozen state or store a copy of thevirtual machine at the particular point in time. The virtualizedinfrastructure manager 199 may then transfer data associated with thevirtual machine (e.g., an image of the virtual machine or a portion ofthe image of the virtual machine) to the storage appliance. The dataassociated with the virtual machine may include a set of files includinga virtual disk file storing contents of a virtual disk of the virtualmachine at the particular point in time and a virtual machineconfiguration file storing configuration settings for the virtualmachine at the particular point in time. The contents of the virtualdisk file may include the operating system used by the virtual machine,local applications stored on the virtual disk, and user files (e.g.,images and word processing documents). In some cases, the virtualizedinfrastructure manager 199 may transfer a full image of the virtualmachine to the storage appliance or a plurality of data blockscorresponding with the full image (e.g., to enable a full image-levelbackup of the virtual machine to be stored on the storage appliance). Inother cases, the virtualized infrastructure manager 199 may transfer aportion of an image of the virtual machine associated with data that haschanged since an earlier point in time prior to the particular point intime or since a last snapshot of the virtual machine was taken. In oneexample, the virtualized infrastructure manager 199 may transfer onlydata associated with changed blocks stored on a virtual disk of thevirtual machine that have changed since the last snapshot of the virtualmachine was taken. In one embodiment, the data management applicationmay specify a first point in time and a second point in time and thevirtualized infrastructure manager 199 may output one or more changeddata blocks associated with the virtual machine that have been modifiedbetween the first point in time and the second point in time.

FIG. 1C depicts one embodiment of a storage appliance, such as storageappliance 170 in FIG. 1A. The storage appliance may include a pluralityof physical machines that may be grouped together and presented as asingle computing system. Each physical machine of the plurality ofphysical machines may comprise a node in a cluster (e.g., a failovercluster). As depicted, the storage appliance 170 includes hardware-levelcomponents and software-level components. The hardware-level componentsinclude one or more physical machines, such as physical machine 120 andphysical machine 130. The physical machine 120 includes a networkinterface 121, processor 122, memory 123, and disk 124 all incommunication with each other. Processor 122 allows physical machine 120to execute computer readable instructions stored in memory 123 toperform processes described herein. Disk 124 may include a hard diskdrive and/or a solid-state drive. The physical machine 130 includes anetwork interface 131, processor 132, memory 133, and disk 134 all incommunication with each other. Processor 132 allows physical machine 130to execute computer readable instructions stored in memory 133 toperform processes described herein. Disk 134 may include a hard diskdrive and/or a solid-state drive. In some cases, disk 134 may include aflash-based SSD or a hybrid HDD/SSD drive. In one embodiment, thestorage appliance 170 may include a plurality of physical machinesarranged in a cluster (e.g., eight machines in a cluster). Each of theplurality of physical machines may include a plurality of multi-coreCPUs, 128 GB of RAM, a 500 GB SSD, four 4 TB HDDs, and a networkinterface controller.

As depicted in FIG. 1C, the software-level components of the storageappliance 170 may include data management system 102, a virtualizationinterface 104, a distributed job scheduler 108, a distributed metadatastore 110, a distributed file system 112, and one or more virtualmachine search indexes, such as virtual machine search index 106. In oneembodiment, the software-level components of the storage appliance 170may be run using a dedicated hardware-based appliance. In anotherembodiment, the software-level components of the storage appliance 170may be run from the cloud (e.g., the software-level components may beinstalled on a cloud service provider).

In some cases, the data storage across a plurality of nodes in a cluster(e.g., the data storage available from the one or more physicalmachines) may be aggregated and made available over a single file systemnamespace (e.g., /snapshots/). A directory for each virtual machineprotected using the storage appliance 170 may be created (e.g., thedirectory for Virtual Machine A may be/snapshots/VM_A). Snapshots andother data associated with a virtual machine may reside within thedirectory for the virtual machine. In one example, snapshots of avirtual machine may be stored in subdirectories of the directory (e.g.,a first snapshot of Virtual Machine A may reside in/snapshots/VM_A/s1/and a second snapshot of Virtual Machine A may residein/snapshots/VM_A/s2/).

The distributed file system 112 may present itself as a single filesystem, in which as new physical machines or nodes are added to thestorage appliance 170, the cluster may automatically discover theadditional nodes and automatically increase the available capacity ofthe file system for storing files and other data. Each file stored inthe distributed file system 112 may be partitioned into one or morechunks. Each of the one or more chunks may be stored within thedistributed file system 112 as a separate file. The files stored withinthe distributed file system 112 may be replicated or mirrored over aplurality of physical machines, thereby creating a load-balanced andfault tolerant distributed file system. In one example, storageappliance 170 may include ten physical machines arranged as a failovercluster and a first file corresponding with a full-image snapshot of avirtual machine (e.g., /snapshots/VM_A/s1/s1.full) may be replicated andstored on three of the ten machines. In some cases, the data chunksassociated with a file stored in the distributed file system 112 mayinclude replicated data (e.g., due to n-way mirroring) or parity data(e.g., due to erasure coding). When a disk storing one of the datachunks fails, then the distributed file system may regenerate the lostdata and store the lost data using a new disk.

In one embodiment, the distributed file system 112 may be used to storea set of versioned files corresponding with a virtual machine. The setof versioned files may include a first file comprising a full image ofthe virtual machine at a first point in time and a second filecomprising an incremental file relative to the full image. The set ofversioned files may correspond with a snapshot chain for the virtualmachine. The distributed file system 112 may determine a first set ofdata chunks that includes redundant information for the first file(e.g., via application of erasure code techniques) and store the firstset of data chunks across a plurality of nodes within a cluster. Theplacement of the first set of data chunks may be determined based on thelocations of other data related to the first set of data chunks (e.g.,the locations of other chunks corresponding with the second file orother files within the snapshot chain for the virtual machine). In someembodiments, the distributed file system 112 may also co-locate datachunks or replicas of virtual machines discovered to be similar to eachother in order to allow for cross virtual machine deduplication. In thiscase, the placement of the first set of data chunks may be determinedbased on the locations of other data corresponding with a differentvirtual machine that has been determined to be sufficiently similar tothe virtual machine.

The distributed metadata store 110 may comprise a distributed databasemanagement system that provides high availability without a single pointof failure. The distributed metadata store 110 may act as a quick-accessdatabase for various components in the software stack of the storageappliance 170 and may store metadata corresponding with stored snapshotsusing a SSD or a Flash-based storage device. In one embodiment, thedistributed metadata store 110 may comprise a database, such as adistributed document oriented database. The distributed metadata store110 may be used as a distributed key value storage system. In oneexample, the distributed metadata store 110 may comprise a distributedNoSQL key value store database. In some cases, the distributed metadatastore 110 may include a partitioned row store, in which rows areorganized into tables or other collections of related data held within astructured format within the key value store database. A table (or a setof tables) may be used to store metadata information associated with oneor more files stored within the distributed file system 112. Themetadata information may include the name of a file, a size of the file,file permissions associated with the file, when the file was lastmodified, and file mapping information associated with an identificationof the location of the file stored within a cluster of physicalmachines. In one embodiment, a new file corresponding with a snapshot ofa virtual machine may be stored within the distributed file system 112and metadata associated with the new file may be stored within thedistributed metadata store 110. The distributed metadata store 110 mayalso be used to store a backup schedule for the virtual machine and alist of snapshots for the virtual machine that are stored using thestorage appliance 170.

In some cases, the distributed metadata store 110 may be used to manageone or more versions of a virtual machine. Each version of the virtualmachine may correspond with a full image snapshot of the virtual machinestored within the distributed file system 112 or an incremental snapshotof the virtual machine (e.g., a forward incremental or reverseincremental) stored within the distributed file system 112. In oneembodiment, the one or more versions of the virtual machine maycorrespond with a plurality of files. The plurality of files may includea single full image snapshot of the virtual machine and one or moreincrementals derived from the single full image snapshot. The singlefull image snapshot of the virtual machine may be stored using a firststorage device of a first type (e.g., a HDD) and the one or moreincrementals derived from the single full image snapshot may be storedusing a second storage device of a second type (e.g., an SSD). In thiscase, only a single full image needs to be stored and each version ofthe virtual machine may be generated from the single full image or thesingle full image combined with a subset of the one or moreincrementals. Furthermore, each version of the virtual machine may begenerated by performing a sequential read from the first storage device(e.g., reading a single file from a HDD) to acquire the full image and,in parallel, performing one or more reads from the second storage device(e.g., performing fast random reads from an SSD) to acquire the one ormore incrementals. In some cases, a first version of a virtual machinecorresponding with a first snapshot of the virtual machine at a firstpoint in time may be generated by concurrently reading a full image forthe virtual machine corresponding with a state of the virtual machineprior to the first point in time from the first storage device whilereading one or more incrementals from the second storage devicedifferent from the first storage device (e.g., reading the full imagefrom a HDD at the same time as reading 64 incrementals from an SSD).

The distributed job scheduler 108 may comprise a distributed faulttolerant job scheduler, in which jobs affected by node failures arerecovered and rescheduled to be run on available nodes. In oneembodiment, the distributed job scheduler 108 may be fully decentralizedand implemented without the existence of a master node. The distributedjob scheduler 108 may run job scheduling processes on each node in acluster or on a plurality of nodes in the cluster and each node mayindependently determine which tasks to execute. The distributed jobscheduler 108 may be used for scheduling backup jobs that acquire andstore virtual machine snapshots for one or more virtual machines overtime. The distributed job scheduler 108 may follow a backup schedule tobackup an entire image of a virtual machine at a particular point intime or one or more virtual disks associated with the virtual machine atthe particular point in time.

The job scheduling processes running on at least a plurality of nodes ina cluster (e.g., on each available node in the cluster) may manage thescheduling and execution of a plurality of jobs. The job schedulingprocesses may include run processes for running jobs, cleanup processesfor cleaning up failed tasks, and rollback processes for rolling-back orundoing any actions or tasks performed by failed jobs. In oneembodiment, the job scheduling processes may detect that a particulartask for a particular job has failed and in response may perform acleanup process to clean up or remove the effects of the particular taskand then perform a rollback process that processes one or more completedtasks for the particular job in reverse order to undo the effects of theone or more completed tasks. Once the particular job with the failedtask has been undone, the job scheduling processes may restart theparticular job on an available node in the cluster.

The virtualization interface 104 may provide an interface forcommunicating with a virtualized infrastructure manager managing avirtualization infrastructure, such as virtualized infrastructuremanager 199 in FIG. 1B, and requesting data associated with virtualmachine snapshots from the virtualization infrastructure. Thevirtualization interface 104 may communicate with the virtualizedinfrastructure manager using an API for accessing the virtualizedinfrastructure manager (e.g., to communicate a request for a snapshot ofa virtual machine).

The virtual machine search index 106 may include a list of files thathave been stored using a virtual machine and a version history for eachof the files in the list. Each version of a file may be mapped to theearliest point in time snapshot of the virtual machine that includes theversion of the file or to a snapshot of the virtual machine thatincludes the version of the file (e.g., the latest point in timesnapshot of the virtual machine that includes the version of the file).In one example, the virtual machine search index 106 may be used toidentify a version of the virtual machine that includes a particularversion of a file (e.g., a particular version of a database, aspreadsheet, or a word processing document). In some cases, each of thevirtual machines that are backed up or protected using storage appliance170 may have a corresponding virtual machine search index.

The data management system 102 may comprise an application running onthe storage appliance that manages the capturing, storing,deduplication, compression (e.g., using a lossless data compressionalgorithm such as LZ4 or LZ77), and encryption (e.g., using a symmetrickey algorithm such as Triple DES or AES-256) of data for the storageappliance 170. In one example, the data management system 102 maycomprise a highest level layer in an integrated software stack runningon the storage appliance. The integrated software stack may include thedata management system 102, the virtualization interface 104, thedistributed job scheduler 108, the distributed metadata store 110, andthe distributed file system 112. In some cases, the integrated softwarestack may run on other computing devices, such as a server or computingdevice 154 in FIG. 1A. The data management system 102 may use thevirtualization interface 104, the distributed job scheduler 108, thedistributed metadata store 110, and the distributed file system 112 tomanage and store one or more snapshots of a virtual machine. Eachsnapshot of the virtual machine may correspond with a point in timeversion of the virtual machine. The data management system 102 maygenerate and manage a list of versions for the virtual machine. Eachversion of the virtual machine may map to or reference one or morechunks and/or one or more files stored within the distributed filesystem 112. Combined together, the one or more chunks and/or the one ormore files stored within the distributed file system 112 may comprise afull image of the version of the virtual machine.

In some embodiments, a plurality of versions of a virtual machine may bestored as a base file associated with a complete image of the virtualmachine at a particular point in time and one or more incremental filesassociated with forward and/or reverse incremental changes derived fromthe base file. The data management system 102 may patch together thebase file and the one or more incremental files in order to generate aparticular version of the plurality of versions by adding and/orsubtracting data associated with the one or more incremental files fromthe base file or intermediary files derived from the base file. In someembodiments, each version of the plurality of versions of a virtualmachine may correspond with a merged file. A merged file may includepointers or references to one or more files and/or one or more chunksassociated with a particular version of a virtual machine. In oneexample, a merged file may include a first pointer or symbolic link to abase file and a second pointer or symbolic link to an incremental fileassociated with the particular version of the virtual machine. In someembodiments, the one or more incremental files may correspond withforward incrementals (e.g., positive deltas), reverse incrementals(e.g., negative deltas), or a combination of both forward incrementalsand reverse incrementals.

FIG. 1D depicts one embodiment of a portion of an integrated datamanagement and storage system that includes a plurality of nodes incommunication with each other and one or more storage devices via one ormore networks 180. The plurality of nodes may be networked together andpresent themselves as a unified storage system. The plurality of nodesincludes node 141 and node 147. The one or more storage devices includestorage device 157 and storage device 158. Storage device 157 maycorrespond with a cloud-based storage (e.g., private or public cloudstorage). Storage device 158 may comprise a hard disk drive (HDD), amagnetic tape drive, a solid-state drive (SSD), a storage area network(SAN) storage device, or a networked-attached storage (NAS) device. Theintegrated data management and storage system may comprise a distributedcluster of storage appliances in which each of the storage appliancesincludes one or more nodes. In one embodiment, node 141 and node 147 maycomprise two nodes housed within a first storage appliance, such asstorage appliance 170 in FIG. 1C. In another embodiment, node 141 maycomprise a first node housed within a first storage appliance and node147 may comprise a second node housed within a second storage appliancedifferent from the first storage appliance. The first storage applianceand the second storage appliance may be located within a data center,such as data center 150 in FIG. 1A, or located within different datacenters.

As depicted, node 141 includes a network interface 142, a nodecontroller 143, and a first plurality of storage devices including HDDs144-145 and SSD 146. The first plurality of storage devices may comprisetwo or more different types of storage devices. The node controller 143may comprise one or more processors configured to store, deduplicate,compress, and/or encrypt data stored within the first plurality ofstorage devices. Node 147 includes a network interface 148, a nodecontroller 149, and a second plurality of storage devices including HDDs151-152 and SSD 153. The second plurality of storage devices maycomprise two or more different types of storage devices. The nodecontroller 149 may comprise one or more processors configured to store,deduplicate, compress, and/or encrypt data stored within the secondplurality of storage devices. In some cases, node 141 may correspondwith physical machine 120 in FIG. 1C and node 147 may correspond withphysical machine 130 in FIG. 1C.

FIGS. 2A-2Q depict various embodiments of sets of files and datastructures (e.g., implemented using merged files) associated withmanaging and storing snapshots of virtual machines.

FIG. 2A depicts one embodiment of a set of virtual machine snapshotsstored as a first set of files. The first set of files may be storedusing a distributed file system, such as distributed file system 112 inFIG. 1C. As depicted, the first set of files includes a set of reverseincrementals (R1-R4), a full image (Base), and a set of forwardincrementals (F1-F2). The set of virtual machine snapshots includesdifferent versions of a virtual machine (versions V1-V7 of VirtualMachine A) captured at different points in time (times T1-T7). In somecases, the file size of the reverse incremental R3 and the file size ofthe forward incremental F2 may both be less than the file size of thebase image corresponding with version V5 of Virtual Machine A. The baseimage corresponding with version V5 of Virtual Machine A may comprise afull image of Virtual Machine A at point in time T5. The base image mayinclude a virtual disk file for Virtual Machine A at point in time T5.The reverse incremental R3 corresponds with version V2 of VirtualMachine A and the forward incremental F2 corresponds with version V7 ofVirtual Machine A. The forward incremental F1 may be associated with thedata changes that occurred to Virtual Machine A between time T5 and timeT6. The forward incremental F1 may include one or more changed datablocks.

In some embodiments, each snapshot of the set of virtual machinesnapshots may be stored within a storage appliance, such as storageappliance 170 in FIG. 1A. In other embodiments, a first set of the setof virtual machine snapshots may be stored within a first storageappliance and a second set of the set of virtual machine snapshots maybe stored within a second storage appliance, such as storage appliance140 in FIG. 1A. In this case, a data management system may extend acrossboth the first storage appliance and the second storage appliance. Inone example, the first set of the set of virtual machine snapshots maybe stored within a local cluster repository (e.g., recent snapshots ofthe file may be located within a first data center) and the second setof the set of virtual machine snapshots may be stored within a remotecluster repository (e.g., older snapshots or archived snapshots of thefile may be located within a second data center) or a cloud repository.

FIG. 2B depicts one embodiment of a merged file for generating versionV7 of Virtual Machine A using the first set of files depicted in FIG.2A. The merged file includes a first pointer (pBase) that references thebase image Base (e.g., via the path/snapshots/VM_A/s5/s5.full), a secondpointer (pF1) that references the forward incremental F1 (e.g., via thepath/snapshots/VM_A/s6/s6.delta), and a third pointer (pF2) thatreferences the forward incremental F2 (e.g., via thepath/snapshots/VM_A/s7/s7.delta). In one embodiment, to generate thefull image of version V7 of Virtual Machine A, the base image may beacquired, the data changes associated with forward incremental F1 may beapplied to (or patched to) the base image to generate an intermediateimage, and then the data changes associated with forward incremental F2may be applied to the intermediate image to generate the full image ofversion V7 of Virtual Machine A.

FIG. 2C depicts one embodiment of a merged file for generating versionV2 of Virtual Machine A using the first set of files depicted in FIG.2A. The merged file includes a first pointer (pBase) that references thebase image Base (e.g., via the path/snapshots/VM_A/s5/s5.full), a secondpointer (pR1) that references the reverse incremental R1 (e.g., via thepath/snapshots/VM_A/s4/s4.delta), a third pointer (pR2) that referencesthe reverse incremental R2 (e.g., via thepath/snapshots/VM_A/s3/s3.delta), and a fourth pointer (pR3) thatreferences the reverse incremental R3 (e.g., via thepath/snapshots/VM_A/s2/s2.delta). In one embodiment, to generate thefull image of version V2 of Virtual Machine A, the base image may beacquired, the data changes associated with reverse incremental R1 may beapplied to the base image to generate a first intermediate image, thedata changes associated with reverse incremental R2 may be applied tothe first intermediate image to generate a second intermediate image,and then the data changes associated with reverse incremental R3 may beapplied to the second intermediate image to generate the full image ofversion V2 of Virtual Machine A.

FIG. 2D depicts one embodiment of a set of virtual machine snapshotsstored as a second set of files after a rebasing process has beenperformed using the first set of files in FIG. 2A. The second set offiles may be stored using a distributed file system, such as distributedfile system 112 in FIG. 1C. The rebasing process may generate new filesR12, R11, and Base2 associated with versions V5-V7 of Virtual Machine Ain order to move a full image closer to a more recent version of VirtualMachine A and to improve the reconstruction time for the more recentversions of Virtual Machine A. The data associated with the full imageBase in FIG. 2A may be equivalent to the new file R12 patched over R11and the full image Base2. Similarly, the data associated with the fullimage Base2 may be equivalent to the forward incremental F2 in FIG. 2Apatched over F1 and the full image Base in FIG. 2A.

The process of moving the full image snapshot for the set of virtualmachine snapshots to correspond with the most recent snapshot versionmay be performed in order to shorten or reduce the chain lengths for thenewest or most recent snapshots, which may comprise the snapshots ofVirtual Machine A that are the most likely to be accessed. In somecases, a rebasing operation (e.g., that moves the full image snapshotfor a set of virtual machine snapshots to correspond with the mostrecent snapshot version) may be triggered when a number of forwardincremental files is greater than a threshold number of forwardincremental files for a snapshot chain (e.g., more than 200 forwardincremental files). In other cases, a rebasing operation may betriggered when the total disk size for the forward incremental filesexceeds a threshold disk size (e.g., is greater than 200 GB) or isgreater than a threshold percentage (e.g., is greater than 20%) of thebase image for the snapshot chain.

In some cases, the rebasing process may be part of a periodic rebasingprocess that is applied at a rebasing frequency (e.g., every 24 hours)to each virtual machine of a plurality of protected virtual machines toreduce the number of forward incremental files that need to be patchedto a base image in order to restore the most recent version of a virtualmachine. Periodically reducing the number of forward incremental filesmay reduce the time to restore the most recent version of the virtualmachine as the number of forward incremental files that need to beapplied to a base image to generate the most recent version may belimited. In one example, if a rebasing process is applied to snapshotsof a virtual machine every 24 hours and snapshots of the virtual machineare acquired every four hours, then the number of forward incrementalfiles may be limited to at most five forward incremental files.

As depicted, the second set of files includes a set of reverseincrementals (R11-R12 and R1-R4) and a full image (Base2). The set ofvirtual machine snapshots includes the different versions of the virtualmachine (versions V1-V7 of Virtual Machine A) captured at the differentpoints in time (times T1-T7) depicted in FIG. 2A. In some cases, thefile size of the reverse incremental R2 may be substantially less thanthe file size of the base image Base2. The reverse incremental R2corresponds with version V2 of Virtual Machine A and the base imageBase2 corresponds with version V7 of Virtual Machine A. In this case,the most recent version of Virtual Machine A (i.e., the most recentrestore point for Virtual Machine A) comprises a full image. To generateearlier versions of Virtual Machine A, reverse incrementals may beapplied to (or patched to) the full image Base2. Subsequent versions ofVirtual Machine A may be stored as forward incrementals that depend fromthe full image Base2.

In one embodiment, a rebasing process may be applied to a first set offiles associated with a virtual machine in order to generate a secondset of files to replace the first set of files. The first set of filesmay include a first base image from which a first version of the virtualmachine may be derived and a first forward incremental file from which asecond version of the virtual machine may be derived. The second set offiles may include a second reverse incremental file from which the firstversion of the virtual machine may be derived and a second base imagefrom which the second version of the virtual machine may be derived.During the rebasing process, data integrity checking may be performed todetect and correct data errors in the files stored in a file system,such as distributed file system 112 in FIG. 1C, that are read togenerate the second set of files.

FIG. 2E depicts one embodiment of a merged file for generating versionV7 of Virtual Machine A using the second set of files depicted in FIG.2D. The merged file includes a first pointer (pBase2) that referencesthe base image Base2 (e.g., via the path/snapshots/VM_A/s7/s7.full). Inthis case, the full image of version V7 of Virtual Machine A may bedirectly acquired without patching forward incrementals or reverseincrementals to the base image Base2 corresponding with version V7 ofVirtual Machine A.

FIG. 2F depicts one embodiment of a merged file for generating versionV2 of Virtual Machine A using the second set of files depicted in FIG.2D. The merged file includes a first pointer (pBase2) that referencesthe base image Base2 (e.g., via the path/snapshots/VM_A/s7/s7.full), asecond pointer (pR11) that references the reverse incremental R11 (e.g.,via the path/snapshots/VM_A/s6/s6.delta), a third pointer (pR12) thatreferences the reverse incremental R12 (e.g., via thepath/snapshots/VM_A/s5/s5.delta), a fourth pointer (pR1) that referencesthe reverse incremental R1 (e.g., via thepath/snapshots/VM_A/s4/s4.delta), a fifth pointer (pR2) that referencesthe reverse incremental R2 (e.g., via thepath/snapshots/VM_A/s3/s3.delta), and a sixth pointer (pR3) thatreferences the reverse incremental R3 (e.g., via thepath/snapshots/VM_A/s2/s2.delta). In one embodiment, to generate thefull image of version V2 of Virtual Machine A, the base image may beacquired, the data changes associated with reverse incremental R11 maybe applied to the base image to generate a first intermediate image, thedata changes associated with reverse incremental R12 may be applied tothe first intermediate image to generate a second intermediate image,the data changes associated with reverse incremental R1 may be appliedto the second intermediate image to generate a third intermediate image,the data changes associated with reverse incremental R2 may be appliedto the third intermediate image to generate a fourth intermediate image,and then the data changes associated with reverse incremental R3 may beapplied to the fourth intermediate image to generate the full image ofversion V2 of Virtual Machine A.

FIG. 2G depicts one embodiment of a set of files associated withmultiple virtual machine snapshots. The set of files may be stored usinga distributed file system, such as distributed file system 112 in FIG.1C. As depicted, the set of files includes a set of reverse incrementals(R1-R3), a full image (Base), and a set of forward incrementals (F1-F2,F3, and F5-F6). In this case, a first version of Virtual Machine B maybe generated using a forward incremental F3 that derives from Version VXof Virtual Machine A and a second version of Virtual Machine C may begenerated using forward incrementals F5-F6 that are derived from VersionVZ of Virtual Machine A. In one example, Virtual Machine B may have beeninitially cloned from Version VX of Virtual Machine A and VirtualMachine C may have been initially cloned from Version VZ of VirtualMachine A.

In one embodiment, in response to a failure of a first virtual machinein a production environment (e.g., due to a failure of a physicalmachine running the first virtual machine), a most recent snapshot ofthe first virtual machine stored within a storage appliance, such asstorage appliance 170 in FIG. 1C, may be mounted and made available tothe production environment. In some cases, the storage appliance mayallow the most recent snapshot of the first virtual machine to bemounted by a computing device within the production environment, such asserver 160 in FIG. 1A. Once the most recent snapshot of the firstvirtual machine has been mounted, data stored within the most recentsnapshot of the first virtual machine may be read and/or modified andnew data may be written without the most recent snapshot of the firstvirtual machine being fully restored and transferred to the productionenvironment. In some cases, a server within the production environmentmay boot up a failed virtual machine directly from a storage appliance,such as storage appliance 170 in FIG. 1C, acting as an NFS datastore tominimize the recovery time to recover the failed virtual machine.

FIG. 2H depicts one embodiment of a merged file for generating versionV1 of Virtual Machine B using the set of files depicted in FIG. 2G. Themerged file includes a first pointer (pBase) that references the baseimage Base, a second pointer (pR1) that references the reverseincremental R1, a third pointer (pR2) that references the reverseincremental R2, and a fourth pointer (pF3) that references the forwardincremental F3. In one embodiment, to generate the full image of versionV1 of Virtual Machine B, the base image associated with Version VY ofVirtual Machine A may be acquired, the data changes associated withreverse incremental R1 may be applied to the base image to generate afirst intermediate image, the data changes associated with reverseincremental R2 may be applied to the first intermediate image togenerate a second intermediate image, and the data changes associatedwith forward incremental F3 may be applied to the second intermediateimage to generate the full image of version V1 of Virtual Machine B.

FIG. 2I depicts one embodiment of a merged file for generating versionV2 of Virtual Machine C using the set of files depicted in FIG. 2G. Themerged file includes a first pointer (pBase) that references the baseimage Base, a second pointer (pF1) that references the forwardincremental F1, a third pointer (pF5) that references the forwardincremental F5, and a fourth pointer (pF6) that references the forwardincremental F6. In one embodiment, to generate the full image of versionV2 of Virtual Machine C, a base image (e.g., the base image associatedwith Version VY of Virtual Machine A) may be acquired, the data changesassociated with forward incremental F1 may be applied to the base imageto generate a first intermediate image, the data changes associated withforward incremental F5 may be applied to the first intermediate image togenerate a second intermediate image, and the data changes associatedwith forward incremental F6 may be applied to the second intermediateimage to generate the full image of version V2 of Virtual Machine C.

FIG. 2J depicts one embodiment of a set of files associated withmultiple virtual machine snapshots after a rebasing process has beenperformed using the set of files in FIG. 2G. The set of files may bestored using a distributed file system, such as distributed file system112 in FIG. 1C. The rebasing process may generate new files R12, R11,and Base2. As depicted, the set of files includes a set of reverseincrementals (R11-R12 and R1-R3), a full image (Base2), and a set offorward incrementals (F3 and F5-F7). In this case, a first version ofVirtual Machine B may be generated using a forward incremental F3 thatderives from Version VX of Virtual Machine A and a second version ofVirtual Machine C may be generated using forward incrementals F5-F6 thatare derived from Version VZ of Virtual Machine A. In one example,Virtual Machine B may have been initially cloned from Version VX ofVirtual Machine A and Virtual Machine C may have been initially clonedfrom version VZ of Virtual Machine A. Forward incremental file F7 mayinclude changes to Version VW of Virtual Machine A that occurredsubsequent to the generation of the full image file Base2. In somecases, the forward incremental file F7 may comprise a writeable file orhave file permissions allowing modification of the file, while all otherfiles associated with earlier versions of Virtual Machine A compriseread only files.

FIG. 2K depicts one embodiment of a merged file for generating versionV1 of Virtual Machine B using the set of files depicted in FIG. 2J. Themerged file includes a first pointer (pBase2) that references the baseimage Base2, a second pointer (pR11) that references the reverseincremental R11, a third pointer (pR12) that references the reverseincremental R12, a fourth pointer (pR1) that references the reverseincremental R1, a fifth pointer (pR2) that references the reverseincremental R2, and a sixth pointer (pF3) that references the forwardincremental F3. In one embodiment, to generate the full image of versionV1 of Virtual Machine B, a base image (e.g., the base image associatedwith Version VW of Virtual Machine A) may be acquired, the data changesassociated with reverse incremental R11 may be applied to the base imageto generate a first intermediate image, the data changes associated withreverse incremental R12 may be applied to the first intermediate imageto generate a second intermediate image, the data changes associatedwith reverse incremental R1 may be applied to the second intermediateimage to generate a third intermediate image, the data changesassociated with reverse incremental R2 may be applied to the thirdintermediate image to generate a fourth intermediate image, and the datachanges associated with forward incremental F3 may be applied to thefourth intermediate image to generate the full image of version V1 ofVirtual Machine B.

FIG. 2L depicts one embodiment of a merged file for generating versionV2 of Virtual Machine C using the set of files depicted in FIG. 2J. Themerged file includes a first pointer (pBase2) that references the baseimage Base2, a second pointer (pR11) that references the reverseincremental R11, a third pointer (pF5) that references the forwardincremental F5, and a fourth pointer (pF6) that references the forwardincremental F6. In one embodiment, to generate the full image of versionV2 of Virtual Machine C, a base image (e.g., the base image associatedwith Version VW of Virtual Machine A) may be acquired, the data changesassociated with reverse incremental R11 may be applied to the base imageto generate a first intermediate image, the data changes associated withforward incremental F5 may be applied to the first intermediate image togenerate a second intermediate image, and the data changes associatedwith forward incremental F6 may be applied to the second intermediateimage to generate the full image of version V2 of Virtual Machine C.

In some cases, a backed-up version of a first virtual machine may begenerated by concurrently reading a full image of a second virtualmachine different from the first virtual machine from a first storagedevice (e.g., a HDD) while reading one or more incrementals associatedwith the first virtual machine from a second storage device (e.g., anSSD) different from the first storage device.

FIG. 2M depicts one embodiment of a set of files associated withmultiple virtual machine snapshots. The set of files may be stored usinga distributed file system, such as distributed file system 112 in FIG.1C. As depicted, the set of files includes a second full image (BaseB),a set of forward incrementals (F1-F2 and F5-F6) that derive from thesecond full image (BaseB), and a set of reverse incrementals (R1-R3)that derive from the second full image (BaseB). The set of files alsoincludes a first full image (BaseA) and a reverse incremental (R4) thatderives from the first full image (BaseA). In this case, the depictedsnapshots for Virtual Machine A include two different full imagesnapshots (BaseA and BaseB). Each of the full image snapshots maycomprise an anchor snapshot for a snapshot chain. The first full image(BaseA) and the reverse incremental (R4) may comprise a first snapshotchain with the first full image acting as the anchor snapshot. A secondsnapshot chain may comprise the second full image (BaseB), the set offorward incrementals (F1-F2), and the set of reverse incrementals(R1-R3). The first snapshot chain and the second snapshot chain may beindependent of each other and independently managed. For example, thebase image associated with the second snapshot chain for Virtual MachineA may be repositioned (e.g., via rebasing) without impacting the firstsnapshot chain for Virtual Machine A.

A third snapshot chain for Virtual Machine C may comprise the secondfull image (BaseB) and forward incrementals (F1 and F5-F6). The firstsnapshot chain for Virtual Machine A and the third snapshot chain forVirtual Machine C may be independent of each other and independentlymanaged. However, as Virtual Machine C is a dependent virtual machinethat depends from the second snapshot chain for Virtual Machine A,changes to the second snapshot chain may impact the third snapshotchain. For example, repositioning of the base image for the secondsnapshot chain due to rebasing may require the merged files for thethird snapshot chain to be updated.

In some embodiments, each of the snapshot chains for Virtual Machine Amay have a maximum incremental chain length (e.g., no more than 100total incremental files), a maximum reverse incremental chain length(e.g., no more than 50 reverse incremental files), and a maximum forwardincremental chain length (e.g., no more than 70 forward incrementalfiles. In the event that a new snapshot will cause one of the snapshotchains to violate the maximum incremental chain length, the maximumreverse incremental chain length, or the maximum forward incrementalchain length, then a new snapshot chain may be created for VirtualMachine A and a new full-image base file may be stored for the newsnapshot chain.

FIG. 2N depicts one embodiment of a merged file for generating versionVS of Virtual Machine A using the set of files depicted in FIG. 2M. Themerged file includes a first pointer (pBaseA) that references the firstbase image BaseA and a second pointer (pR4) that references the reverseincremental R4. In one embodiment, to generate the full image of versionVS of Virtual Machine A, the first base image associated with Version VTof Virtual Machine A may be acquired and the data changes associatedwith reverse incremental R4 may be applied to the first base image togenerate the full image of version VS of Virtual Machine A.

FIG. 2O depicts one embodiment of a merged file for generating versionVU of Virtual Machine A using the set of files depicted in FIG. 2M. Themerged file includes a first pointer (pBaseB) that references the secondbase image BaseB, a second pointer (pR1) that references the reverseincremental R1, a third pointer (pR2) that references the reverseincremental R2, and a fourth pointer (pR3) that references the reverseincremental R3. In one embodiment, to generate the full image of versionVU of Virtual Machine A, the second base image associated with VersionVY of Virtual Machine A may be acquired, the data changes associatedwith reverse incremental R1 may be applied to the second base image togenerate a first intermediate image, the data changes associated withreverse incremental R2 may be applied to the first intermediate image togenerate a second intermediate image, and the data changes associatedwith reverse incremental R3 may be applied to the second intermediateimage to generate the full image of version VU of Virtual Machine A.

FIG. 2P depicts one embodiment of a set of files associated withmultiple virtual machine snapshots after a rebasing process has beenperformed to a snapshot chain using the set of files in FIG. 2M. The setof files may be stored using a distributed file system, such asdistributed file system 112 in FIG. 1C. The rebasing process maygenerate new files R12, R11, and BaseB2. As depicted, the set of filesincludes a set of reverse incrementals (R11-R12 and R1-R2), a full image(BaseB2), and a set of forward incrementals (F5-F7). In this case, asecond version of Virtual Machine C may be generated using forwardincrementals F5-F6 that are derived from Version VZ of Virtual MachineA. Forward incremental file F7 may include changes to Version VW ofVirtual Machine A that occurred subsequent to the generation of the fullimage file BaseB2. In some cases, the forward incremental file F7 maycomprise a writeable file or have file permissions allowing modificationof the file, while all other files associated with earlier versions ofVirtual Machine A comprise read only files.

FIG. 2Q depicts one embodiment of a merged file for generating versionVU of Virtual Machine A using the set of files depicted in FIG. 2P. Themerged file includes a first pointer (pBaseA) that references the firstbase image BaseA and a second pointer (pF9) that references the forwardincremental F9. In one embodiment, to generate the full image of versionVU of Virtual Machine A, the first base image associated with Version VTof Virtual Machine A may be acquired and the data changes associatedwith forward incremental F9 may be applied to the first base image togenerate the full image of version VU of Virtual Machine A.

In some embodiments, upon detection that a second snapshot chain hasreached a maximum incremental chain length (e.g., no more than 500 totalincremental files), a maximum reverse incremental chain length (e.g., nomore than 400 reverse incremental files), or a maximum forwardincremental chain length (e.g., no more than 150 forward incrementalfiles), an existing snapshot chain (e.g., the first snapshot chaindepicted in FIG. 2P) may have its chain length extended or snapshotspreviously assigned to the second snapshot chain may be moved to theexisting snapshot chain. For example, the first snapshot chain depictedin FIG. 2M comprises two total snapshots, while the first snapshot chaindepicted in FIG. 2P comprises three total snapshots as the snapshotcorresponding with version VU of Virtual Machine A has moved from thesecond snapshot chain to the first snapshot chain.

In some embodiments, the number of snapshots in a snapshot chain maydecrease over time as older versions of a virtual machine areconsolidated, archived, deleted, or moved to a different storage domain(e.g., to cloud storage) depending on the data backup and archivingschedule for the virtual machine. In some cases, the maximum incrementalchain length or the maximum number of snapshots for a snapshot chain maybe increased over time as the versions stored by the snapshot chain age.In one example, if the versions of a virtual machine stored using asnapshot chain are all less than one month old, then the maximumincremental chain length may be set to a maximum of 200 incrementals;however, if the versions of the virtual machine stored using thesnapshot chain are all greater than one month old, then the maximumincremental chain length may be set to a maximum of 1000 incrementals.

In some embodiments, the maximum incremental chain length for a snapshotchain may be increased over time as the number of allowed snapshots in asnapshot chain may be increased as the backed-up versions of a virtualmachine get older. For example, the maximum incremental chain length fora snapshot chain storing versions of a virtual machine that are lessthan one year old may comprise a maximum incremental chain length of 200incrementals, while the maximum incremental chain length for a snapshotchain storing versions of a virtual machine that are more than one yearold may comprise a maximum incremental chain length of 500 incrementals.

In some embodiments, the maximum incremental chain length, the maximumreverse incremental chain length, or the maximum forward incrementalchain length for a snapshot chain may be adjusted over time as nodes ordisks are added to or removed from a cluster or upon an update to a databackup and archiving schedule for a virtual machine due to theassignment of a new backup class or a new backup, replication, andarchival policy. In one example, the maximum incremental chain lengthmay be increased from 200 incrementals to 500 incrementals if the numberof nodes or disks falls below a threshold number (e.g., is less thanfour nodes). In another example, the maximum incremental chain lengthmay be increased from 100 incrementals to 200 incrementals if theavailable disk storage falls below a threshold amount if disk space(e.g., the amount of available disk space is less than 20 TB).

FIG. 3A is a flowchart describing one embodiment of a process formanaging and storing virtual machine snapshots using a data storagesystem. In one embodiment, the process of FIG. 3A may be performed by astorage appliance, such as storage appliance 170 in FIG. 1A.

In step 302, a schedule for backing up a first virtual machine isdetermined. In one example, the schedule for backing up the firstvirtual machine may comprise periodically backing up the first virtualmachine every four hours. The schedule for backing up the first virtualmachine may be derived from a new backup, replication, and archivalpolicy or backup class assigned to the first virtual machine. In step304, a job scheduler is configured to implement the schedule for backingup the first virtual machine. In one example, a distributed jobscheduler, such as distributed job scheduler 108 in FIG. 1C, may beconfigured to schedule and run processes for capturing and storingimages of the first virtual machine over time according the schedule. Instep 306, a snapshot process for acquiring a snapshot of the firstvirtual machine is initiated. The snapshot process may send aninstruction to a virtualized infrastructure manager, such asvirtualization manager 169 in FIG. 1A, that requests data associatedwith the snapshot of the first virtual machine. In step 308, a type ofsnapshot to be stored is determined. The type of snapshot may comprise afull image snapshot or an incremental snapshot. In some cases, a fullimage snapshot may be captured and stored in order to serve as an anchorsnapshot for a new snapshot chain. Versions of the first virtual machinemay be stored using one or more independent snapshot chains, whereineach snapshot chain comprises a full image snapshot and one or moreincremental snapshots. One embodiment of a process for determining thetype of snapshot to be stored (e.g., storing either a full imagesnapshot or an incremental snapshot) is described later in reference toFIG. 3B.

In step 310, it is determined whether a full image of the first virtualmachine needs to be stored in order to store the snapshot of the firstvirtual machine. The determination of whether a full image is requiredmay depend on whether a previous full image associated with a priorversion of the first virtual machine has been acquired. Thedetermination of whether a full image is required may depend on thedetermination of the type of snapshot to be stored in step 308. If afull image needs to be stored, then step 311 is performed. Otherwise, ifa full image does not need to be stored, then step 312 is performed. Instep 311, the full image of the first virtual machine is acquired. Thefull image of the first virtual machine may correspond with a file orone or more data chunks. In step 312, changes relative to a priorversion of the first virtual machine or relative to another virtualmachine (e.g., in the case that the first virtual machine comprises adependent virtual machine whose snapshots derive from a full imagesnapshot of a second virtual machine different from the first virtualmachine) are acquired. The changes relative to the prior version of thefirst virtual machine or relative to a version of a different virtualmachine may correspond with a file or one or more data chunks. In step313, the full image of the first virtual machine is stored using adistributed file system, such as distributed file system 112 in FIG. 1C.In step 314, the changes relative to the prior version of the firstvirtual machine or relative to another virtual machine are stored usinga distributed file system, such as distributed file system 112 in FIG.1C. In one embodiment, the full image of the first virtual machine maybe stored using a first storage device of a first type (e.g., a HDD) andthe changes relative to the prior version of the first virtual machinemay be stored using a second storage device of a second type (e.g., anSSD).

In some embodiments, snapshots of the first virtual machine may beingested at a snapshot capture frequency (e.g., every 30 minutes) by adata storage system. When a snapshot of the first virtual machine isingested, the snapshot may be compared with other snapshots storedwithin the data storage system in order to identify a candidate snapshotfrom which the snapshot may depend. In one example, a scalableapproximate matching algorithm may be used to identify the candidatesnapshot whose data most closely matches the data associated with thesnapshot or to identify the candidate snapshot whose data has the fewestnumber of data differences with the snapshot. In another example, anapproximate matching algorithm may be used to identify the candidatesnapshot whose data within a first portion of the candidate snapshotmost closely matches data associated with a first portion of thesnapshot. In some cases, a majority of the data associated with thesnapshot and the candidate snapshot may be identical (e.g., both thesnapshot and the candidate snapshot may be associated with virtualmachines that use the same operation system and have the sameapplications installed). Once the candidate snapshot has beenidentified, then data differences (or the delta) between the snapshotand the candidate snapshot may be determined and the snapshot may bestored based on the data differences. In one example, the snapshot maybe stored using a forward incremental file that includes the datadifferences between the snapshot and the candidate snapshot. The forwardincremental file may be compressed prior to being stored within a filesystem, such as distributed file system 112 in FIG. 1C.

In step 316, a merged file associated with the snapshot is generated.The merged file may reference one or more files or one or more datachunks that have been acquired in either step 311 or step 312. In oneexample, the merged file may comprise a file or a portion of a file thatincludes pointers to the one or more files or the one or more datachunks. In step 318, the merged file is stored in a metadata store, suchas distributed metadata store 110 in FIG. 1C. In step 320, a virtualmachine search index for the first virtual machine is updated. Thevirtual machine search index for the first virtual machine may include alist of files that have been stored in the first virtual machine and aversion history for each of the files in the list. In one example, thevirtual machine search index for the first virtual machine may beupdated to include new files that have been added to the first virtualmachine since a prior snapshot of the first virtual machine was takenand/or to include updated versions of files that were previously storedin the first virtual machine.

FIG. 3B is a flowchart describing one embodiment of a process fordetermining the type of snapshot to be stored using a data storagesystem. The process described in FIG. 3B is one example of a process forimplementing step 308 in FIG. 3A. In one embodiment, the process of FIG.3B may be performed by a storage appliance, such as storage appliance170 in FIG. 1A.

In step 332, a snapshot chain for a first virtual machine is identified.The snapshot chain may comprise a full image snapshot for the firstvirtual machine and one or more incremental snapshots that derive fromthe full image snapshot. Backed-up versions of the first virtual machinemay correspond with one or more snapshot chains. Each of the one or moresnapshot chains may include a full image snapshot or a base image fromwhich incremental snapshots may derive. One example of backed-upversions of a virtual machine being stored using one or more snapshotchains is depicted in FIG. 2P in which the versions of Virtual Machine Aare stored using a first snapshot chain anchored by full image BaseA anda second snapshot chain anchored by full image BaseB2.

In step 334, it is determined whether the snapshot chain includes adependent base file. In this case, the first virtual machine maycomprise a dependent virtual machine that has snapshots that derive froma full image snapshot of a different virtual machine. In one embodiment,the first virtual machine and the different virtual machine from whichthe first virtual machine depends may each have different virtualmachine configuration files for storing configuration settings for thevirtual machines. In one example, the first virtual machine may have afirst number of virtual processors (e.g., two processors) and thedifferent virtual machine may have a second number of virtual processorsdifferent from the first number of virtual processors (e.g., fourprocessors). In another example, the first virtual machine may have afirst virtual memory size (e.g., 1 GB) and the different virtual machinemay have a second virtual memory size different from the first virtualmemory size (e.g., 2 GB). In another example, the first virtual machinemay run a first guest operating system and the different virtual machinemay run a second guest operating system different from the first guestoperating system.

In step 336, a maximum incremental chain length for the snapshot chainis determined based on whether the snapshot chain includes a dependentbase file. In one example, if the first virtual machine comprises adependent virtual machine, then the maximum incremental chain length maybe set to a maximum length of 200 snapshots; however if the firstvirtual machine is independent and is not a dependent virtual machine,then the maximum incremental chain length may be set to a maximum lengthof 500 snapshots.

In one embodiment, the maximum incremental chain length for the snapshotchain may be determined based on an age of the backed-up versions withinthe snapshot chain. In one example, the maximum incremental chain lengthfor a snapshot chain storing versions of the first virtual machine thatare less than one year old may comprise a maximum incremental chainlength of 100 incrementals, while the maximum incremental chain lengthfor a snapshot chain storing versions of the first virtual machine thatare more than one year old may comprise a maximum incremental chainlength of 200 incrementals.

In step 338, it is determined whether a new snapshot chain should becreated based on the maximum incremental chain length. In step 340, atype of snapshot to be stored for the first virtual machine isdetermined based on the maximum incremental chain length. The type ofsnapshot may comprise either a full image snapshot or an incrementalsnapshot. In one embodiment, if the snapshot chain for the first virtualmachine exceeds the maximum incremental chain length for the snapshotchain, then the type of snapshot to be stored for the first virtualmachine may comprise a full image snapshot. In this case, an additionalsnapshot chain may be created for the first virtual machine.

FIG. 3C is a flowchart describing one embodiment of a process forrestoring a version of a virtual machine using a data storage system. Inone embodiment, the process of FIG. 3C may be performed by a storageappliance, such as storage appliance 170 in FIG. 1A.

In step 382, a particular version of a virtual machine to be restored isidentified. In step 384, a base image from which the particular versionmay be derived is determined. In step 386, a set of incremental filesfor generating the particular version is determined. In one embodiment,the base image and the set of incremental files may be determined from amerged file associated with the particular version of the virtualmachine. In some cases, the set of incremental files may include one ormore forward incremental files and one or more reverse incrementalfiles. In step 388, a file associated with the particular version isgenerated using the base image and the set of incremental files. Thefile may be generated by patching the set of incremental files onto thebase image.

In one example, referring to FIG. 2G, if the particular version of thevirtual machine corresponds with Version V2 of Virtual Machine C, thenthe base image may correspond with the file Base in FIG. 2G and the setof incremental files may correspond with files F1, F5, and F6 of FIG.2G. In another example, referring to FIG. 2G, if the particular versioncorresponds with Version V1 of Virtual Machine B, then the base imagemay correspond with the file Base in FIG. 2G and the set of incrementalfiles may correspond with files R1, R2, and F3 of FIG. 2G. The set ofincremental files may include a first subset of incremental filescorresponding with the virtual machine (e.g., Virtual Machine C) and asecond subset of incremental files corresponding with a second virtualmachine (e.g., Virtual Machine A) different from the virtual machine. Instep 390, at least a portion of the file is outputted. The at least theportion of the file (e.g., 100 GB of the file) may be electronicallytransferred to a computing device, such as computing device 154 in FIG.1A, or to a virtualization manager, such as virtualization manager 169in FIG. 1A.

In some embodiments, the base image and a subset of the set ofincremental files may correspond with a second virtual machine differentfrom the virtual machine. In this case, the base image may comprise thebase image for the second virtual machine and the set of incrementalfiles may include a dependent base file that comprises data differencesbetween the base image for the second virtual machine and a previouslyacquired base image for the virtual machine. Referring to FIG. 2G, theincremental file F5 may comprise a dependent base file for VirtualMachine C and the incremental file F3 may comprise a dependent base filefor Virtual Machine B. Data deduplication techniques may be applied toidentify a candidate base image from which a dependent base file maydepend and to generate the dependent base file.

FIG. 4A depicts one embodiment of a distributed semaphore comprisingthree semaphores for reserving disk space that may be allocated to jobsrunning on data storage nodes within a cluster. The data storage nodesmay include nodes 141 and 147 in FIG. 1D. Each semaphore of thedistributed semaphore may correspond with a unique key for accessing thesemaphore. As depicted, if the total disk space for the clustercomprises 48 TBs of disk space, then a first semaphore 402 of the threesemaphores may be used to reserve disk space within a range of 0-16 TBof disk space, a second semaphore 403 of the three semaphores may beused to reserve disk space within a range of 16 TB-32 TB of disk space,and a third semaphore 404 of the three semaphores may be used to reservedisk space within a range of 32 TB-48 TB of disk space.

In one embodiment, a job to be run using the cluster may use thedistributed semaphore to reserve and/or allocate an amount of disk spacerequired by the job during execution of the job prior to the job beingexecuted by a node within the cluster. A job scheduler, such as thedistributed job scheduler 108 in FIG. 1C, may identify the job prior toassignment of the job to the node within the cluster and may utilize acomputing process to reserve the amount of disk space required by thejob during execution of the job using the distributed semaphore. In oneexample, the job may require 24 TBs of disk space during execution ofthe job and may reserve the 24 TBs of disk space using the firstsemaphore 402 and the second semaphore 403. After the job has been run,the reserved disk space may be unreserved or freed from reservation andmade available to subsequent jobs. In the case that the 24 TBs of diskspace are reserved using the entire first semaphore 402 and the entiresecond semaphore 403, 8 TBs of disk space may be unnecessarily reservedfor the job.

The distributed semaphore may be stored using one or more tables thatare stored using a distributed key-value store or a distributed metadatastore, such as the distributed metadata store 110 in FIG. 1C. Thedistributed key-value store may comprise a distributed NoSQL key-valuestore database. Each of the semaphores within the distributed semaphoremay correspond with a unique identifier or a unique key for accessing ormodifying the semaphore. Each of the semaphores within the distributedsemaphore may correspond with a different row in a table for thedistributed semaphore. The table may be stored using the distributedkey-value store. In one example, the distributed semaphore may append alinear identifier to a global name for the distributed semaphore to eachof the individual semaphores. In this case, the first semaphore 402 maybe identified as “SEM_1,” the second semaphore 403 may be identified as“SEM_2,” and the third semaphore 404 may be identified as “SEM_3.” Inone embodiment, a semaphore of the distributed semaphore may comprise abinary semaphore or a mutex. The semaphore may include a variable thatmay be set in order to provide mutually exclusive access to a particularresource, such as the allocation of a portion of a disk space to a job.The variable may be set into an available or unavailable state for theresource. The variable may be set into a reserved or unreserved statefor the portion of the disk space. In some cases, the variable may beset into a reserved, pending reservation, or unreserved state for theportion of the disk space.

One benefit of increasing the number of semaphores for the distributedsemaphore is that the load on each semaphore or the load on each rowwithin a table for the distributed semaphore may be reduced. As thenumber of semaphores increases, the number of times that each semaphoreof the distributed semaphore is accessed may be reduced. However,increasing the number of semaphores may lead to an increase infragmentation of allocated disk space, which may adversely impactperformance.

FIG. 4B depicts one embodiment of a distributed semaphore comprisingfour semaphores for reserving disk space accessible by data storagenodes within a cluster. As the number of nodes within the cluster mayvary over time (e.g., due to nodes being added or removed from thecluster), the total disk space available to jobs running within thecluster may also vary over time. As depicted, if the total disk spacefor the cluster comprises 64 TBs of disk space, then the threesemaphores 402-403 may be used to reserve disk space within the range of0-48 TBs and a fourth semaphore 405 may be used to reserve disk spacewithin a range of 48-64 TBs.

In some cases, on a periodic basis (e.g., every ten minutes), the numberof semaphores within the distributed semaphore may be adjusted or setbased on the number of nodes within a cluster or based on the totalamount of disk space corresponding with the nodes within the cluster. Inone example, the number of semaphores may comprise a total amount ofdisk space divided by 16 TBs per semaphore. In other cases, the numberof semaphores within the distributed semaphore may be fixed and thetotal amount of disk space that may be reserved may be evenly dividedper semaphore (e.g., the total amount of disk space may be evenlydivided among ten semaphores).

FIG. 4C depicts another embodiment of a distributed semaphore comprisingfour semaphores for reserving disk space accessible by data storagenodes within a cluster. As depicted, if the total disk space for thecluster comprises 48 TBs of disk space, then a first semaphore 412 ofthe four semaphores may be used to reserve disk space within a range of0-12 TB of disk space, a second semaphore 413 of the four semaphores maybe used to reserve disk space within a range of 12 TB-24 TB of diskspace, a third semaphore 414 of the four semaphores may be used toreserve disk space within a range of 24 TB-36 TB of disk space, and afourth semaphore 415 of the four semaphores may be used to reserve diskspace within a range of 36 TB-48 TB of disk space.

In some cases, on a periodic basis or upon detection that a node hasbeen added to or removed from a cluster, the number of contention failsmay be determined based on the number of times that jobs failed toallocate adequate disk space from the distributed semaphore over aparticular period of time (e.g., over the past ten minutes). As thenumber of contention fails associated with jobs that have failed toaccess the distributed semaphore or have failed to reserve the requiredamount of disk space changes over time, the number of semaphores for thedistributed semaphore may be adjusted such that the number of contentionfails is between an upper threshold (e.g., not more than 100 contentionfails over a ten minute period of time) and a lower threshold (e.g.,more than ten contention fails over the ten minute period of time). Incases where the number of contention fails is less than the lowerthreshold, then the number of semaphores may be reduced in order toreduce fragmentation of the disk space. In cases where the number ofcontention fails is greater than the upper threshold, then the number ofsemaphores may be increased in order to reduce the number of contentionfails.

In one embodiment, upon detection that the number of contention failsover the particular period of time has exceeded the upper threshold, thenumber of semaphores may be increased from three semaphores, such as thedistributed semaphore with three semaphores depicted in FIG. 4A, to foursemaphores, such as the distributed semaphore with four semaphoresdepicted in FIG. 4C.

FIG. 4D depicts one embodiment of a distributed semaphore comprising sixsemaphores for reserving disk space accessible by data storage nodeswithin a cluster. As depicted, if the total disk space for the clustercomprises 48 TBs of disk space, then the six semaphores 422-427 may beused to cover 8 TB disk spaces within the range of 0-48 TBs of diskspace. In one embodiment, upon detection that the number of contentionfails over a particular period of time has exceeded an upper thresholdby at least ten contention failures, the number of semaphores may beincreased from three semaphores, such as the distributed semaphore withthree semaphores depicted in FIG. 4A, to six semaphores, such as thedistributed semaphore with six semaphores depicted in FIG. 4D. If thenumber of contention fails over the particular period of time exceededthe upper threshold, then the number of semaphores may be increased fromthree semaphores, such as the distributed semaphore with threesemaphores depicted in FIG. 4A, to four semaphores, such as thedistributed semaphore with four semaphores depicted in FIG. 4C. Inanother embodiment, upon detection that the number of contention failsover the particular period of time was less than ten contention failuresor less than a lower threshold, the number of semaphores may bedecreased from six semaphores to three semaphores (e.g., cut in half).As the number of semaphores is decreased, the amount of disk spacecovered by each of the semaphores may increase (e.g., from covering 8TBs of disk space to covering 16 TBs of disk space).

FIG. 4E depicts one embodiment of the distributed semaphore depicted inFIG. 4A with fixed-size chunks per semaphore. As the first semaphore 402covers 16 TBs of disk space, each chunk of the four data chunks 431-434covers 4 TBs of disk space. In some cases, each of the semaphores withinthe distributed semaphore may have the same number of chunks and each ofthe chunks may be of the same fixed size (e.g., each of the chunks maycover 4 TBs or 10 TBs of disk space). Each of the chunks within asemaphore may correspond with a different variable that may be set tospecify whether the disk space corresponding with the chunk is pending,reserved, or unreserved.

FIG. 4F depicts another embodiment of the distributed semaphore depictedin FIG. 4A with different-sized chunks per semaphore. As depicted, thefirst semaphore 402 includes two chunks 436-437 that each cover 8 TBs ofdisk space, the second semaphore 403 includes four chunks 441-444 thateach cover 4 TBs of disk space, and the third semaphore 404 includes twochunks 451-452 that each cover 4 TBs of disk space and a third chunk 453that covers 8 TBs of disk space.

The determination of chunk sizes may be made on a per distributedsemaphore basis such that every chunk within the distributed semaphorecovers the same amount of disk space. In one example, each of the chunksfor the distributed semaphore depicted in FIG. 4E may comprise chunksassociated with 4 TBs of disk space. In another example, the chunk sizefor each of the chunks within the distributed semaphore may be set basedon the amount of available disk space that has not yet been allocated tojobs running within the cluster. If the amount of available disk spaceis below a threshold amount of disk space (e.g., there is less than 20TBs of available disk space), then the chunk size may be cut in half orreduced in order to improve utilization of the remaining available diskspace. In some cases, the chunk sizes corresponding with unreservedchunks within a semaphore may be cut in half if the amount of availabledisk space is detected to be less than the threshold amount of diskspace. As an example, the chunk 453 for the third semaphore depicted inFIG. 4E may have been marked as reserved and therefore the reduction inchunk size only created the two chunks 451-452. Conversely, if theamount of available disk space is greater than the threshold amount ofdisk space, then the chunk size may be increased (e.g., doubled insize).

The determination of chunk sizes may be made on a per semaphore basis.In one embodiment, the chunk size may be set based on an amount ofreservable disk space associated with the disk space covered by thesemaphore. In one example, if the amount of reservable disk space (e.g.,the amount of disk space that has not been marked as taken or reservedand is available to be reserved by a job) is greater than a thresholdamount of disk space (e.g., is more than 8 TBs of disk space), then thechunk size may be set to 8 TBs of disk space; otherwise, if the amountof reservable disk space is less than or equal to the threshold amountof disk space, then the chunk size may be set to 4 TBs of disk space.Reducing the chunk size as the amount of reservable disk space decreasesmay improve utilization of the allocated disk space.

FIG. 4G depicts one embodiment of the distributed semaphore depicted inFIG. 4E over time as disk space for a job is reserved. The job mayrequire 16 TBs of disk space during execution of the job. At time T1,the distributed semaphore may have two chunks 431 and 433 of the firstsemaphore 402 marked as reserved and two chunks 432 and 434 marked asunreserved or available. The second semaphore 403 may have two chunks441 and 444 marked as reserved and two chunks 442-443 marked asunreserved. The third semaphore 404 may have three chunks 451-452 and454 marked as reserved and one chunk 453 marked as unreserved.

The job (or a process working on behalf of the job) may identify aninitial semaphore for reserving the required 16 TBs of disk space. Theinitial semaphore may be identified using a job identifier for the job(e.g., via the job identifier modulo the number of semaphores within thedistributed semaphore). The job may then attempt to reserve as much ofthe required 16 TBs of disk space from the initial semaphore. In thiscase, the job may reserve at most 8 TBs of the 16 TBs. At time T2, thechunks 432 and 434 for the first semaphore 402 have been marked asreserved for the job. The job may then identify another semaphore of thedistributed semaphore that has the greatest amount of reservable diskspace. In this case, the second semaphore 403 comprises the semaphorewith the greatest amount of reservable disk space. However, rather thanreserving the entire 8 TBs that may be reserved from the secondsemaphore 403, the job may only reserve 4 Tbs in order to leavereservable disk space available to jobs that directly map to the secondsemaphore 403 as their initial semaphore. In one example, a reservedchunk size (e.g., set to 4 TBs of disk space) may be acquired and thejob may attempt to reserve as much disk space as possible from thesecond semaphore 403 up to the amount of disk space reservable by thesecond semaphore 403 minus the reserved chunk size. At time T3, thechunk 442 for the second semaphore 403 has been reserved. At time T4,the chunk 453 for the third semaphore 404 has been reserved. Upondetection that the required 16 TBs of disk space has been reserved, the16 TBs of disk space corresponding with the reserved portions of thedistributed semaphore may be allocated to the job. The job may maintaina list of the semaphores and/or the chunks within each of the semaphoresused to obtain the allocated disk space and use the list to release thesemaphores and the reserved chunks upon completion of the job. The jobmay release the semaphores and the reserved chunks by marking thereserved chunks as unreserved or available.

FIG. 5A depicts one embodiment of initial mappings from jobs to initialsemaphores. As depicted, jobs 512-513 map to the first semaphore 402,jobs 514-515 map to the second semaphore 403, and jobs 516-517 map tothe third semaphore 404. The initial mappings may be used to identifythe initial semaphore (or the first semaphore) of the distributedsemaphore to which a job may attempt to reserve as much of its requireddisk space as possible.

FIG. 5B depicts another embodiment of initial mappings from jobs toinitial semaphores. As depicted, jobs 512 and 515 map to the firstsemaphore 402, jobs 513 and 516 map to the second semaphore 403, andjobs 514 and 517 map to the third semaphore 404. The initial mappingfrom a particular job to its initial semaphore of a distributedsemaphore may comprise a hash function. The initial mapping may map ajob identifier for the particular job to one of the semaphores withinthe distributed semaphore. In one example, the initial mapping maycomprise acquiring the job identifier for the job and computing the jobidentifier modulo N, where N is the number of semaphores within thedistributed semaphore. In some cases, if it is detected that a thresholdnumber of initial semaphores are completely reserved or that a thresholdnumber of jobs were not able to reserve any disk space from theirinitial semaphores, then the initial mapping may be modified. In oneexample, if it is detected that 100 jobs have mapped to initialsemaphores that were completely reserved within the past ten minutes,then the initial mapping may be updated to be the job identifier plus anoffset modulo N, where N is the number of semaphores within thedistributed semaphore. In another example, if it is detected that 50jobs have mapped to initial semaphores that were completely reservedwithin the past ten minutes, then the initial mappings may be changedfrom the initial mappings depicted in FIG. 5B to the initial mappingsdepicted in FIG. 5A.

FIG. 6A is a flowchart describing one embodiment of a process forallocating disk space using a distributed semaphore. In one embodiment,the process of FIG. 6A may be performed by a storage appliance, such asstorage appliance 170 or storage appliance 140 in FIG. 1A. The processof FIG. 6A may be performed by a data storage node, such as node 141 inFIG. 1D.

In step 602, a first job to be run that requires an amount of disk spaceis identified. In one example, a job scheduler, such as the distributedjob scheduler 108 in FIG. 1C, may identify the first job. The first jobmay comprise a job for capturing and storing a snapshot of a real orvirtual machine. The amount of disk space required by the first job maydepend upon the size of the snapshot to be stored. In step 604, aninitial semaphore mapping associated with the first job is acquired. Theinitial semaphore mapping may provide a mapping for the first job to afirst semaphore (or an initial semaphore) of a distributed semaphoreused for reserving disk space. The initial semaphore mapping may map ajob identifier for the first job to the first semaphore. In one example,the initial semaphore mapping may map the job identifier for the firstjob modulo the number of semaphores within the distributed semaphore tothe first semaphore.

In step 606, a first semaphore of a plurality of semaphores forreserving disk space is identified based on the initial semaphoremapping. In step 608, a first portion of the amount of disk space isreserved from the first semaphore. In one example, the first semaphoremay correspond with the first semaphore 402 in FIG. 4G and thereservation of the first portion may correspond with the reservations ofchunks 432 and 434 at time T2 in FIG. 4G. In some cases, the firstportion of the amount of disk space may be reserved by marking chunkswithin the first semaphore as reserved. In other cases, the chunkswithin the first semaphore may be marked as pending allocation and maybe marked as reserved once the entire amount of disk space required bythe first job has been reserved or allocated.

In step 610, it is detected that the first portion of the amount of diskspace is less than the amount of disk space required by the first job.In this case, the entire amount of disk space required by the first jobcannot be reserved using only the first semaphore. In step 612, a subsetof the plurality of semaphores is identified. In one embodiment, thesubset of the plurality of semaphores may be randomly selected from theplurality of semaphores (e.g., via the random selection of threesemaphores out of the plurality of semaphores). In another embodiment,the subset of the plurality of semaphores may be determined as the threesemaphores out of the plurality of semaphores with the greatest amountof available disk space to be reserved. In some cases, the number ofsemaphores for the subset of the plurality of semaphores may bedetermined based on the amount of reservable disk space that may bereserved from the subset. In step 614, a second semaphore of the subsetof the plurality of semaphores is identified. The second semaphore maycorrespond with the semaphore out of the subset with the greatest amountof available disk space or the greatest number of chunks that are notmarked as reserved or pending allocation.

In step 616, a reserved chunk size for the second semaphore isdetermined. The reserved chunk size may correspond with an amount ofdisk space that is to be left available for other jobs to reserve. Inone example, the reserved chunk size may correspond with a thresholdpercentage of the amount of disk space covered by the second semaphore(e.g., the reserved chunk size may comprise twenty percent of the amountof disk space covered by the second semaphore). In another example, thereserved chunk size may be determined based on a historical amount ofdisk space required by jobs that directly map to the second semaphore orfor which the second semaphore comprises the initial semaphore.

In step 618, a second portion of the amount of disk space is reservedfrom the second semaphore. The second portion of the amount of diskspace may comprise the remaining amount of disk space required by thefirst job. In some cases, the second portion of the amount of disk spacemay be reserved only if the second portion of the amount of disk spacemay be reserved from the second semaphore leaving disk space associatedwith the reserved chunk size available or unreserved. In step 620, it isdetected that the amount of disk space required by the first job hasbeen reserved using the plurality of semaphores. Upon detection that theamount of disk space required by the first job has been reserved usingthe distributed semaphore, the amount of disk space required by thefirst job may be allocated to the first job. In step 622, the first jobis run subsequent to allocating the amount of disk space required by thefirst job to the first job. The first job may be executed using a datastorage node within a cluster of data storage nodes and the amount ofdisk space may be allocated from available disk space within the clusterof data storage nodes.

In some embodiments, in cases where the amount of disk space required bya first job cannot be reserved from a first semaphore or the initialsemaphore for the first job, the remaining amount of disk space to bereserved for the first job may be allocated sequentially starting withsemaphores of the distributed semaphore with the greatest amount of freedisk space or the greatest amount of unreserved disk space after diskspace reservation have been made to the initial semaphore.

FIGS. 6B-6C depict a flowchart describing another embodiment of aprocess for allocating disk space using a distributed semaphore. In oneembodiment, the process of FIGS. 6B-6C may be performed by a storageappliance, such as storage appliance 170 or storage appliance 140 inFIG. 1A. The process of FIGS. 6B-6C may be performed by a data storagenode, such as node 141 in FIG. 1D.

In step 632, a total amount of a resource associated with a plurality ofnodes within a cluster is determined. In some cases, the cluster maycomprise a plurality of data storage nodes and the resource maycorrespond with the amount of disk space for the cluster. In othercases, the resource may correspond with a global network bandwidthallowance for the cluster. In step 634, a number of contention failsassociated with jobs that failed to access a distributed semaphore thatoccurred during a particular period of time is determined. Theparticular period of time may comprise the past ten minutes. In step636, a number of semaphores corresponding with the distributed semaphoreis determined based on the number of contention fails and/or the totalamount of the resource. The distributed semaphore may comprise aplurality of semaphores for reserving portions of the resource. In oneexample, the number of semaphores may be set such that the amount of theresource reservable by each of the semaphores is a fixed amount (e.g.,each of the semaphores may correspond with 10 TBs of disk space or 10Mbit/s of network bandwidth). In another example, the number ofsemaphores may be set such that the number of contention fails is lessthan a maximum threshold of contention fails (e.g., is less than 100contention fails over a preceding ten minute period of time).

In step 638, it is determined that a job to be run using the clusterrequires a first amount of the resource during execution of the job. Instep 640, a first semaphore of the plurality of semaphores isidentified. The first semaphore may be identified using an initialsemaphore mapping or via a hash function that hashes a job identifierfor the job to the first semaphore. In cases where the first semaphoreis full or completely reserved, a variable tracking the number of fullinitial semaphores may be incremented. In step 642, a first portion ofthe first amount of the resource is reserved using the first semaphore.In step 644, it is detected that the first portion of the first amountof the resource is less than the first amount of the resource requiredby the job during execution. In this case, the entire first amount ofthe resource may not be reserved using only the first semaphore. In step646, a subset of the plurality of semaphores is identified. The subsetmay be identified by randomly selecting five of the plurality ofsemaphores or by identifying the five semaphores of the plurality ofsemaphores with the greatest number of unreserved chunks. In step 648,the subset of the plurality of semaphores is ranked based on an amountof the resource available per semaphore. In step 650, a second semaphoreof the subset of the plurality of semaphores is identified. The secondsemaphore may comprise the semaphore of the subset with the greatestnumber of unreserved chunks or the greatest number of unreservedportions of the resource.

In step 652, a second portion of the first amount of the resource isreserved using the second semaphore. In step 654, it is detected thatthe combination of the first portion and the second portion is less thanthe first amount of the resource required by the job during execution.In step 656, the subset of the plurality of semaphores is ranked againbased on the amount of the resource available per semaphore subsequentto the second portion being reserved using the second semaphore. In step658, a third semaphore of the subset of the plurality of semaphores isidentified. The third semaphore may comprise the semaphore of the subsetwith the greatest number of unreserved chunks or the greatest number ofunreserved portions of the resource subsequent to performing step 656.In step 670, the third portion of the first amount of the resource isreserved using the third semaphore. In step 672, it is detected that thefirst amount of the resource required by the job has been reserved usingthe plurality of semaphores. In step 674, the first amount of theresource is allocated to the job. In step 676, the job is run subsequentallocating the first amount of the resource to the job. The job may beexecuted using a data storage node within the cluster and the job maystore data (e.g., a captured snapshot of a virtual machine) using thefirst amount of the resource (e.g., using 48 TBs of disk spaceassociated with one or more disks).

FIG. 7A is a flowchart describing one embodiment of a process forallocating disk space using a distributed semaphore. In one embodiment,the process of FIG. 7A may be performed by a storage appliance, such asstorage appliance 170 or storage appliance 140 in FIG. 1A. The processof FIG. 7A may be performed by a data storage node, such as node 141 inFIG. 1D.

In step 702, a total amount of disk space for a cluster of data storagenodes at a first point in time is determined. In one example, the totalamount of disk space for the cluster at the first point in time maycomprise 100 TBs of disk space. The disk space may include disk spacefrom HDDs and/or SSDs. In step 704, a first number of semaphorescorresponding with a distributed semaphore is determined based on thetotal amount of disk space for the cluster at the first point in time.In one example, the first number of semaphores may comprise tensemaphores and each of the ten semaphores may correspond with 10 TBs ofdisk space. In step 706, it is detected that the total amount of diskspace for the cluster at a second point in time has changed subsequentto the first point in time. In one example, the total amount of diskspace for the cluster may have increased due to the addition of a nodeto the cluster. In another example, the total amount of disk space forthe cluster may have decreased due to a node failure or due to theremoval of a node from the cluster. In step 708, a second number ofsemaphores corresponding with the distributed semaphore is determinedbased on the total amount of disk space for the cluster at the secondpoint in time. In one example, the second number of semaphores maycomprise twenty semaphores and each of the twenty semaphores maycorrespond with 10 TBs of disk space.

In step 710, a plurality of semaphores for the distributed semaphorecomprising the second number of semaphores is generated. In oneembodiment, the distributed semaphore with the second number ofsemaphores may be stored as a table with a number of rows correspondingwith the second number of semaphores. The plurality of semaphores may bestored using a distributed key-value store. In step 712, disk spacereservations are mapped from a prior set of semaphores comprising thefirst number of semaphores into the plurality of semaphores. In oneexample, the first number of semaphores may comprise three semaphoresand the prior set of semaphores may correspond with the three semaphores402-404 depicted in FIG. 4A. The second number of semaphores maycomprise six semaphores and the plurality of semaphores may correspondwith the six semaphores 422-427 depicted in FIG. 4D. In this case, eachsemaphore of the prior set of semaphores may be split into twosemaphores. In one example, the first half of the first semaphore 402 inFIG. 4A may map to the semaphore 422 in FIG. 4D and the second half ofthe first semaphore 402 in FIG. 4A may map to the semaphore 423 in FIG.4D. If the semaphore 402 in FIG. 4A has been marked as reserved, thenboth the semaphores 422-423 in FIG. 4D may be marked as reserved.

In step 714, a portion of the total amount of disk space for a first jobis reserved using the plurality of semaphores. The portion of the totalamount of disk space for the first job may comprise 50 TBs of disk spacerequired by the first job during execution of the first job. In step716, the portion of the total amount of disk space is allocated to thefirst job. In step 718, the first job is run using the cluster and datagenerated by the first job is stored using the allocated disk space. Inone example, the first job may generate a full image snapshot of avirtual machine and store the full image snapshot of the virtual machineusing the 50 TBs of disk space allocated to the first job.

FIG. 7B is a flowchart describing another embodiment of a process forallocating disk space using a distributed semaphore. In one embodiment,the process of FIG. 7B may be performed by a storage appliance, such asstorage appliance 170 or storage appliance 140 in FIG. 1A. The processof FIG. 7B may be performed by a data storage node, such as node 141 inFIG. 1D.

In step 732, a total amount of disk space corresponding with a clusterof data storage nodes is determined. In step 734, a number of semaphoresfor a plurality of semaphores is determined based on the total amount ofdisk space. The plurality of semaphores may be used to reserve portionsof the total amount of disk space. In one example, the number ofsemaphores may comprise the total amount of disk space within thecluster divided by 10 TBs of disk space per semaphore; in the case thatthe total amount of disk space within the cluster comprises 100 TBs ofdisk space, the number of semaphores may comprise ten semaphores. Instep 736, an amount of available disk space corresponding with thecluster that is available for allocation to one or more jobs executed bythe cluster is determined. In some cases, the amount of available diskspace corresponding with the cluster may be determined from theunreserved portions of the plurality of semaphores.

In step 738, a chunk size for a first semaphore of the plurality ofsemaphores is determined based on the amount of available disk space. Inone example, if the amount of available disk space for the cluster isabove a threshold amount (e.g., is greater than 48 TBs of disk space),then the chunk size may be set to a first chunk size (e.g., 16 TB);however if the amount of available disk space is less than or equal tothe threshold amount, then the chunk size may be set to a second chunksize (e.g., 8 TB) different from the first chunk size. The second chunksize may be less than the first chunk size.

In step 740, a first job to be run that requires an amount of disk spaceduring execution of the first job is identified. In step 742, a firstportion of the amount of disk space required by the first job isreserved by setting one or more chunks of the chunk size for the firstsemaphore into a pending state. In step 746, it is detected that theamount of disk space required by the first job may be allocated usingthe plurality of semaphores. In one example, it may be detected that theamount of disk space required by the first job may be allocated if a setof chunks within the plurality of semaphores have been set into apending state or a pending allocation state and the disk space coveredby the set of chunks is equal to or greater than the amount of diskspace required by the first job. In step 748, the one or more chunks forthe first semaphore are set into a taken state or a reserved state. Instep 750, the amount of disk space is allocated to the first job. Instep 752, the first job is run using the cluster and data generated bythe first job is stored using the allocated disk space. In one example,the first job may generate a full image snapshot of a real machine andstore the full image snapshot of the real machine using 24 TBs of diskspace allocated to the first job. In another example, the first job maygenerate an incremental file associated with a snapshot of a virtualmachine by consolidating two of more snapshots of the virtual machineand store the incremental file using the disk space allocated to thefirst job.

One embodiment of the disclosed technology includes identifying a firstjob to be executed using a node within a cluster, determining an amountof disk space to be allocated to the first job prior to the first jobbeing executed using the node, identifying an initial semaphore of aplurality of semaphores for reserving disk space, reserving a firstportion of the amount of disk space from the initial semaphore,detecting that the first portion of the amount of disk space is lessthan the amount of disk space to be allocated to the first job,identifying a subset of the plurality of semaphores in response todetecting that the first portion of the amount of disk space is lessthan the amount of disk space to be allocated to the first job, rankingthe subset of the plurality of semaphores based on an amount ofreservable disk space per semaphore, identifying a second semaphore ofthe subset of the plurality of semaphores based on the ranking of thesubset, reserving a second portion of the amount of disk space from thesecond semaphore, detecting that the amount of disk space to beallocated to the first job has been reserved using the plurality ofsemaphores, allocating the amount of disk space to the first job, andexecuting the first job using the node subsequent to allocating theamount of disk space to the first job.

One embodiment of the disclosed technology includes determining that afirst job to be run using a cluster of data storage nodes requires afirst amount of a cluster resource during execution of the first job andidentifying a first semaphore of a plurality of semaphores correspondingwith a distributed semaphore. The plurality of semaphores comprises afirst number of semaphores. The identifying the first semaphore includesidentifying the first semaphore based on a job identifier for the firstjob modulo the first number of semaphores. The method further comprisesreserving a first portion of the first amount of the cluster resourceusing the first semaphore, detecting that the first portion of the firstamount the cluster resource is less than the first amount of theresource required by the first job during execution, identifying asubset of the plurality of semaphores, ranking the subset of theplurality of semaphores based on an amount of the cluster resourceavailable for reservation per semaphore, identifying a second semaphoreof the subset of the plurality of semaphores based on the ranking of thesubset, reserving a second portion of the first amount of the clusterresource using the second semaphore, detecting that the first amount ofthe cluster resource required by the first job has been reserved usingthe plurality of semaphores, allocating the first amount of the clusterresource to the first job, running the first job using the cluster ofdata storage nodes subsequent to allocating the first amount of thecluster resource to the first job, and storing data generated by thefirst job using the cluster of data storage nodes.

One embodiment of the disclosed technology includes a memory (e.g., avolatile or non-volatile memory) in communication with one or moreprocessors. The memory configured to store a plurality of semaphorescorresponding with a distributed semaphore. The one or more processorsconfigured to identify a first job to be executed using a node within acluster. The first job requires an amount of disk space to be allocatedto the first job. The one or more processors configured to identify aninitial semaphore of the plurality of semaphores and reserve a firstportion of the amount of disk space from the first semaphore. The one ormore processors configured to detect that the first portion of theamount of disk space is less than the amount of disk space required bythe first job and identify a subset of the plurality of semaphores. Theone or more processors configured to rank the subset of the plurality ofsemaphores based on an amount of reservable disk space per semaphore andidentify a second semaphore of the subset of the plurality of semaphoresbased on the ranking of the subset. The one or more processorsconfigured to reserve a second portion of the amount of disk space fromthe second semaphore and detect that the amount of disk space requiredby the first job has been reserved using the distributed semaphore. Theone or more processors configured to cause the amount of disk spacerequired by the first job to be allocated to the first job and cause thefirst job to be executed on the node subsequent to allocation of theamount of disk space to the first job.

One embodiment of the disclosed technology includes determining a firstamount of disk space for a cluster of data storage nodes at a firstpoint in time, determining a first number of semaphores correspondingwith a distributed semaphore based on the first amount of disk space forthe cluster at the first point in time, determining a second amount ofdisk space for the cluster of data storage nodes at a second point intime subsequent to the first point in time, detecting that the secondamount of disk space for the cluster of data storage nodes at the secondpoint in time is different from the first amount of disk space for thecluster of data storage nodes at the first point in time, anddetermining a second number of semaphores different from the firstnumber of semaphores corresponding with the distributed semaphore inresponse to detecting that the second amount of disk space for thecluster of data storage nodes at the second point in time is differentfrom the first amount of disk space for the cluster of data storagenodes at the first point in time. The determining the second number ofsemaphores includes determining the second number of semaphores based onthe second amount of disk space for the cluster at the second point intime. The method further comprises generating a plurality of semaphorescomprising the second number of semaphores, mapping disk spacereservations from a prior set of semaphores for the distributedsemaphore comprising the first number of semaphores into the pluralityof semaphores comprising the second number of semaphores, reserving aportion of the second amount of disk space for a first job using theplurality of semaphores, allocating the portion of the second amount ofdisk space to the first job, running the first job using the clustersubsequent to allocating the portion of the second amount of disk spaceto the first job, and storing data generated by the first job within theportion of the second amount of disk space allocated to the first job.

One embodiment of the disclosed technology includes determining a totalamount of disk space for a cluster of data storage nodes at a firstpoint in time, determining a first number of semaphores correspondingwith a distributed semaphore based on the total amount of disk space forthe cluster, storing a first plurality of semaphores for the distributedsemaphore comprising the first number of semaphores, detecting that anumber of contention fails associated with prior jobs that failed toaccess the distributed semaphore during a particular period of timesubsequent to the first point in time has exceeded a threshold number ofcontention fails, determining a second number of semaphores greater thanthe first number of semaphores corresponding with the distributedsemaphore subsequent to the first point in time in response to detectingthat the number of contention fails during the particular period of timehas exceeded the threshold number of contention fails, storing a secondplurality of semaphores for the distributed semaphore comprising thesecond number of semaphores, mapping disk space reservations from thefirst plurality of semaphores to the second plurality of semaphores,reserving a portion of the total amount of disk space for a first jobusing the second plurality of semaphores, allocating the portion of thetotal amount of disk space to the first job, running the first job usingthe cluster subsequent to allocating the portion of the total amount ofdisk space to the first job, and storing data generated by the first jobwithin the portion of the total amount of disk space allocated to thefirst job. In some cases, the first number of semaphores may comprisethree semaphores, the second number of semaphores may comprise sixsemaphores, and the mapping of the disk space reservations from thefirst plurality of semaphores to the second plurality of semaphores mayinclude mapping the first half of the first semaphore 402 in FIG. 4A tothe semaphore 422 in FIG. 4D and the second half of the first semaphore402 in FIG. 4A to the semaphore 423 in FIG. 4D.

One embodiment of the disclosed technology includes determining a totalamount of disk space for a cluster of data storage nodes, determining anumber of semaphores for a plurality of semaphores based on the totalamount of disk space, determining an amount of available disk space forthe cluster that is available for allocation, determining a chunk sizefor a first semaphore of the plurality of semaphores based on the amountof available disk space for the cluster, identifying a first job to berun using the cluster that requires a first amount of disk space,reserving a first portion of the first amount of disk space by settingone or more chunks of the chunk size within the first semaphore into apending state, detecting that a plurality of chunks within the pluralityof semaphores covering the first amount of disk space has been set intothe pending state, setting the plurality of chunks within the pluralityof semaphores into a reserved state in response to detecting that theplurality of chunks covering the first amount of disk space has been setinto the pending state, allocating the first amount of disk space to thefirst job, running the first job using the cluster subsequent toallocating the first amount of disk space to the first job, and storingdata generated by the first job using the first amount of disk spaceallocated to the first job.

The disclosed technology may be described in the context ofcomputer-executable instructions, such as software or program modules,being executed by a computer or processor. The computer-executableinstructions may comprise portions of computer program code, routines,programs, objects, software components, data structures, or other typesof computer-related structures that may be used to perform processesusing a computer. In some cases, hardware or combinations of hardwareand software may be substituted for software or used in place ofsoftware.

Computer program code used for implementing various operations oraspects of the disclosed technology may be developed using one or moreprogramming languages, including an object oriented programming languagesuch as Java or C++, a procedural programming language such as the “C”programming language or Visual Basic, or a dynamic programming languagesuch as Python or JavaScript. In some cases, computer program code ormachine-level instructions derived from the computer program code mayexecute entirely on an end user's computer, partly on an end user'scomputer, partly on an end user's computer and partly on a remotecomputer, or entirely on a remote computer or server.

For purposes of this document, it should be noted that the dimensions ofthe various features depicted in the Figures may not necessarily bedrawn to scale.

For purposes of this document, reference in the specification to “anembodiment,” “one embodiment,” “some embodiments,” or “anotherembodiment” may be used to describe different embodiments and do notnecessarily refer to the same embodiment.

For purposes of this document, a connection may be a direct connectionor an indirect connection (e.g., via another part). In some cases, whenan element is referred to as being connected or coupled to anotherelement, the element may be directly connected to the other element orindirectly connected to the other element via intervening elements. Whenan element is referred to as being directly connected to anotherelement, then there are no intervening elements between the element andthe other element.

For purposes of this document, the term “based on” may be read as “basedat least in part on.”

For purposes of this document, without additional context, use ofnumerical terms such as a “first” object, a “second” object, and a“third” object may not imply an ordering of objects, but may instead beused for identification purposes to identify different objects.

For purposes of this document, the term “set” of objects may refer to a“set” of one or more of the objects.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A method for operating a data management system,comprising: identifying a first job to be executed using a node within acluster; determining an amount of disk space to be allocated to thefirst job prior to the first job being executed using the node;identifying an initial semaphore of a plurality of semaphores forreserving disk space; reserving a first portion of the amount of diskspace from the initial semaphore; detecting that the first portion ofthe amount of disk space is less than the amount of disk space to beallocated to the first job; identifying a subset of the plurality ofsemaphores in response to detecting that the first portion of the amountof disk space is less than the amount of disk space to be allocated tothe first job; ranking the subset of the plurality of semaphores basedon an amount of reservable disk space per semaphore; identifying asecond semaphore of the subset of the plurality of semaphores based onthe ranking of the subset; reserving a second portion of the amount ofdisk space from the second semaphore; detecting that the amount of diskspace to be allocated to the first job has been reserved using theplurality of semaphores; allocating the amount of disk space to thefirst job; and executing the first job using the node subsequent toallocating the amount of disk space to the first job.
 2. The method ofclaim 1, wherein: the executing the first job using the node causes asnapshot of a virtual machine to be stored using at least a portion ofthe amount of disk space allocated to the first job.
 3. The method ofclaim 1, wherein: the plurality of semaphores comprises a first numberof semaphores; and the identifying the initial semaphore of theplurality of semaphores includes identifying the initial semaphore basedon a job identifier for the first job modulo the first number ofsemaphores.
 4. The method of claim 1, wherein: the identifying thesecond semaphore of the subset of the plurality of semaphores includesdetecting that the second semaphore comprises a semaphore of the subsetwith a greatest amount of reservable disk space out of the semaphores ofthe subset.
 5. The method of claim 1, further comprising: determining areserved chunk size for the second semaphore; and the reserving thesecond portion of the amount of disk space from the second semaphorecomprises reserving the second portion of the amount of disk space fromthe second semaphore while leaving disk space corresponding with thereserved chunk size unreserved.
 6. The method of claim 1, furthercomprising: acquiring an initial semaphore mapping associated with thefirst job and identifying the initial semaphore using the initialsemaphore mapping.
 7. The method of claim 1, further comprising: storingdata generated by the first job using at least a portion of the amountof disk space allocated to the first job.
 8. The method of claim 7,wherein: the first job corresponds with consolidating two or moresnapshots of a virtual machine; and the storing data generated by thefirst job includes storing the two or more snapshots of the virtualmachine using the at least the portion of the amount of disk spaceallocated to the first job.
 9. The method of claim 1, wherein: theplurality of semaphores comprises a distributed semaphore that is storedusing a distributed key-value store.
 10. The method of claim 1, wherein:each semaphore of the plurality of semaphores corresponds with adifferent portion of disk space within the cluster.
 11. A method foroperating a data management system, comprising: determining that a firstjob to be run using a cluster of data storage nodes requires a firstamount of a cluster resource during execution of the first job;identifying a first semaphore of a plurality of semaphores correspondingwith a distributed semaphore, the plurality of semaphores comprises afirst number of semaphores, the identifying the first semaphore includesidentifying the first semaphore based on a job identifier for the firstjob modulo the first number of semaphores; reserving a first portion ofthe first amount of the cluster resource using the first semaphore;detecting that the first portion of the first amount the clusterresource is less than the first amount of the resource required by thefirst job during execution; identifying a subset of the plurality ofsemaphores; ranking the subset of the plurality of semaphores based onan amount of the cluster resource available for reservation persemaphore; identifying a second semaphore of the subset of the pluralityof semaphores based on the ranking of the subset; reserving a secondportion of the first amount of the cluster resource using the secondsemaphore; detecting that the first amount of the cluster resourcerequired by the first job has been reserved using the plurality ofsemaphores; allocating the first amount of the cluster resource to thefirst job; running the first job using the cluster of data storage nodessubsequent to allocating the first amount of the cluster resource to thefirst job; and storing data generated by the first job using the clusterof data storage nodes.
 12. The method of claim 11, wherein: the firstamount of the cluster resource comprises a first amount of disk spacerequired by the first job during execution of the first job.
 13. Themethod of claim 11, further comprising: determining a number ofcontention fails associated with prior jobs that failed to access thedistributed semaphore during a particular period of time; anddetermining the first number of semaphores based on the number ofcontention fails.
 14. The method of claim 11, further comprising:determining a total amount of disk space for the cluster of data storagenodes; and determining the first number of semaphores based on the totalamount of disk space for the cluster.
 15. The method of claim 11,wherein: the identifying the second semaphore of the subset of theplurality of semaphores includes identifying a semaphore of the subsetwith a greatest amount of reservable disk space out of the semaphores ofthe subset.
 16. The method of claim 11, further comprising: determininga reserved chunk size for the second semaphore; and the reserving thesecond portion of the first amount of the cluster resource using thesecond semaphore includes reserving disk space from the second semaphoresuch that the second semaphore retains other disk space correspondingwith the reserved chunk size unreserved.
 17. A data management system,comprising: a memory configured to store a plurality of semaphorescorresponding with a distributed semaphore; and one or more processorsconfigured to identify a first job to be executed using a node within acluster, the first job requires an amount of disk space to be allocatedto the first job, the one or more processors configured to identify aninitial semaphore of the plurality of semaphores and reserve a firstportion of the amount of disk space from the first semaphore, the one ormore processors configured to detect that the first portion of theamount of disk space is less than the amount of disk space required bythe first job and identify a subset of the plurality of semaphores, theone or more processors configured to rank the subset of the plurality ofsemaphores based on an amount of reservable disk space per semaphore andidentify a second semaphore of the subset of the plurality of semaphoresbased on the ranking of the subset, the one or more processorsconfigured to reserve a second portion of the amount of disk space fromthe second semaphore and detect that the amount of disk space requiredby the first job has been reserved using the distributed semaphore, theone or more processors configured to cause the amount of disk spacerequired by the first job to be allocated to the first job and cause thefirst job to be executed on the node subsequent to allocation of theamount of disk space to the first job.
 18. The data management system ofclaim 17, wherein: the plurality of semaphores comprises a first numberof semaphores; and the one or more processors configured to identify theinitial semaphore based on a job identifier for the first job modulo thefirst number of semaphores.
 19. The data management system of claim 17,wherein: the execution of the first job causes a snapshot of a virtualmachine to be stored within the allocated amount of disk space for thefirst job.
 20. The data management system of claim 17, wherein: the oneor more processors configure to detect that the second semaphorecomprises a semaphore of the subset with a greatest amount of reservabledisk space out of the semaphores of the subset.